Attic is one of the new-generation hash-backup tools (like obnam, zbackup, Vembu Hive etc). It provides encrypted incremental-forever (unlike duplicity, duplicati, rsnapshot, rdiff-backup, Ahsay etc) with no server-side processing and a convenient CLI interface, and it does let you prune old backups.
All other common tools seem to fail on one of the following points
- Incremental forever (bandwidth is expensive in a lot of countries)
- Untrusted remote storage (so i can hook it up to a dodgy lowendbox VPS)
- Optional: No server-side processing needed (so i can hook it up to S3 or Dropbox)
If your backup model is based on the old' original + diff(original, v1) + diff(v1, v2).. then you're going to have a slow time restoring. rdiff-backup gets this right by reversing the incremental chain. However, as soon as you need to consolidate incremental images, you lose the possibility of encrypting the data (since encrypt(diff()) is useless from a diff perspective).
But with a hash-based backup system? All restore points take constant time to restore.
Duplicity, Duplicati 1.x, and Ahsay 5 don't support incremental-forever. Ahsay 6 supports incremental-forever at the expense of requiring trust in the server (server-side decrypt to consolidate images). Duplicati 2 attempted to move to a hash-based system but they chose to use fixed block offsets rather than checksum-based offsets, so the incremental detection is inefficient after an insert point.
IMO Attic gets everything right. There's patches for windows support on their github. I wrote a munin plugin for it.
Sorry, but "Untrusted remote storage" and "No server-side processing" are exactly the opposite of what I need.
If the original box is ever compromised, I don't want the attacker to gain any access to the backup. If you use a dumb storage like S3 as your backup server, you need to store your keys on the original box, and anyone who gains control of the original box can destroy your S3 bucket as well. Ditto for any SSH-based backup scheme that requires keys to be stored on the original box. A compromised box could also lie about checksums, silently corrupting your backups.
Backups should be pulled from the backup box, not pushed from the original box. Pushing backups is only acceptable for consumer devices, and even then, only because we don't have a reliable way to pull data from them (due to frequently changing IP addresses, NAT, etc).
The backup box needs to be even more trustworthy than the original box, not the other way around. I'm willing to live with a significant amount of overhead, both in storage and in bandwidth, in order not to violate this principle.
The backup box, of course, could push encrypted data to untrusted storage, such as S3. But only after it has pulled from the original box. In both cases, the connection is initiated from the backup box, not the other way around. The backup box never accepts any incoming connection.
Does Attic support this kind of use case? The documentation doesn't seem to have anything to say about backing up remote files to local repositories. I don't see any reason why it won't be supported (since rsync does), but "nominally supported" is different from "optimized for that use case", and I suspect that many of the latest generation of backup tools are optimized for the opposite use case.
"Attic can initialize and access repositories on remote hosts if the host is accessible using SSH."
Fantastic. Will work perfectly here. We[1] are happy to support this just like we've supported duplicity all of these years. EDIT: appears obnam also works over plain old SSH. Can't tell about zbackup, however...
As always, email us to discuss the "HN Readers" discount.
If someone is looking at trying attic and wants something a little nicer to configure and run than the very basic shell script from attic's Quick Start[1], check out the wrapper script I wrote to make this a little easier[2]. It's still somewhat "1.0" right now, but it does the basics for me. See the included sample config files for an idea of how the configuration works.[3]
from what i can tell here: https://github.com/c4rlo/attic/commit/f4804c07caac3d145f49fc... ... attic updates the atime when opening files right now... that patche fixes the problem, but i have to wonder how fast it actually and accurate is. bup has all sorts of helpers and tweaks to make it really fast, but also to ensure that it doesn't touch the filesystem while making backups.
i've been amazed to notice how all my files have atimes from july, when i stopped using rsync to make backups and switched to bup. :p
I've long been a huge fan up bup, and have even contributed some code. I might be by far their single biggest user, since I host 96748 bup repositories at https://cloud.sagemath.com, where the snapshots for all user projects are made using bup (and mounted using bup-fuse).
Elsewhere in this discussion people not some shortcomings of bup, namely not having its own encryption and not having the ability to delete old backups. For my applications, lack of encryption isn't an issue, since I make the backups locally on a full-disk encrypted device and transmit them for longterm storage (to another full disk encrypted device) only with ssh. The lack of being able to easily delete old backups is also not an issue since (1) I don't want to delete them (I want a complete history), and (2) the approach to deduplication and compression in bup makes it extremely efficient space wise, and it doesn't get (noticeably) slower as the number of commits gets large; this is in contrast to ZFS, where performance can degrade dramatically if you make a large number of snapshots, or other much less space efficient approaches where you have to regularly delete backups or you run out of space.
In this discussion people also discuss ZFS and deduplication. With SageMathCloud, the filesystem all user projects use is a de-duplicated ZFS-on-Linux filesystem (most on an SSD), with lz4 compression and rolling snapshots (using zfssnap). This configuration works well in practice, since projects have limited quota so there's only a few hundred gigabytes of data (so far less than even 1TB), but the machines have quite a lot of RAM (50+GB) since they are configured for lots of mathematics computation, running IPython notebooks, etc.
I've also been using bup to replace (in some areas) my use of rdiff-backup.
It's a great tool, but since you contributed already, I cannot understate the importance of pruning old archives. For online/disk-based backup solutions, space is always going to run out eventually.
I'm using bup where I already know the backup size will grow in a way that I can manage for the next 1-2 years.
For "classical" backup scenarios though, where binaries and many changes are involved and the backup grows by roughly 10-20% a week due to changes alone, I have to resort to tools where I can prune old archives because I would either have to reduce the number of increments (which I don't want to do) or increase the backup space by a factor of 50x (which I practically cannot do either).
Others have complained here that bup doesn't support deleting old backups. ddar doesn't have such an issue. Deleting snapshots work just fine (all other snapshots remain).
I think the underlying difference is that ddar uses sqlite to keep track of the chunks, whereas bup is tied to git's pack format, which isn't really geared towards large backups. git's pack files are expected to be rewritten, which works fine for code repositories but not for terabytes of data.
It's true that git's pack files are made for being rewritten, but bup doesn't do that. Every new run will create a new pack along with its .idx (which means that some packs may be quasi-empty) and the size of packs is capped at 1GB (Giga, not Gibi).
The real struggle of bup is how to know whether a hash is already stored, and how to know it screaming fast. It could be interesting to compare bup style and standard sqlite style, as you do in ddar.
Also, it seems ddar stores each object in its own file, like git loose objects. SQLite has a page [0] that compares this and storing blobs in SQLite, and I don't know what's the median size of your objects but if it's < 20k it seems to be better to just store them as blobs.
Is there anything out there that does continuous incremental backups to a remote location (like obnam, attic, ...) but allows "append only" access. That is, you are only allowed to add to the backup, and the network protocol inherently does not allow past history to be deleted or modified? Pruning old backups might be allowed, but only using credentials that are reserved for special use.
Obnam, attic and similar use a normal read/write disk area, without any server side processing, so presumably an errant/malicious user is free to delete the entire backup?
Haven't seen this mentioned - but, since bup de-duplicates chunks (and thus may take very little space - e.g., when you backup a 40GB virtual machine, each snapshots takes little more than the actual changes inside the virtual machine), every byte of the backup is actually very important and fragile, as it may be referenced from thousands of files and of snapshots. This is of course true for all dedupping and incremental backups.
However, bup goes one step farther and has builtin support for "par2" which adds error correction - in a way, it efficiently re-duplicates chunks so that whichever one (or two, or however many you decide) break, you can still recover the complete backup.
I saw "par2" and got all excited to see if lelutin re-implemented all the Galois field goodness from scratch, looked at the source and - no, bup merely spawns the par2 binary. Damn :)
I was wondering if someone's done a side-by-side comparison of the various newer open-source backup tools? Specifically, I'm looking for performance, compression, encryption, type of deduplication (file-level vs. block-level, and dedup between generations only vs. dedup across all files). Also, the specifics of the implementation, since some of the tools don't really explain that too well, along with any unique features.
The reason I ask, is I had a difficult time finding a backup tool that suited my own needs, so I wrote and open-sourced my own (http://www.snebu.com), and now that some people are starting to use it in production I'd like to get a deeper peer review to ensure quality and feature completeness. (I actually didn't think I'd be this nervous about people using any of my code, but backups are kind of critical so it I'd like to ensure it is done as correct as possible).
Like any good hacker I got tired of other solutions that didn't quite match my needs and made my own dropbox-like backup/sync using only rsync, ssh and encfs.
- only runs on machines I control
- server requirement is only rsync, ssh and coreutils
- basic conflict detection
- encfs --reverse to encrypt locally, store remotely
- history is rsnapshot-style hard links
- inspect history using sshfs
- can purge old history
shell aliases showing how I use it are in my config repository
encfs isn't ideal but it's the only thing that does the job. Ideally I'd use something that didn't leak so much, but it doesn't exist.
I tried some backup software (of the rdiff variety, not the amanda variety) last year when I set up a small backup server for friends and family.
Obnam and bup seemed to work mostly the way I wanted to but obnam was by far the most mature tool, so this is what I chose in the end.
On the plus side, it provides both push and pull modes. Encryption and expiration works. The minus points are no Windows support, and some horror stories about performance. Apparently it can slow to a crawl with many files. I haven't run into that problem despite hundreds of gig in the backup set, but most are large files.
On the whole it's been very stable and unobtrusive during the time I've used it, but I haven't used it in anger yet. So a careful recommendation for obnam from me.
Does anyone use zpaq[1]? It has compression, deduplication, incremental backup, encryption, backup versioning (unlike bup, with the ability to delete old ones), and its written un C++. But im not sure about performance over network and how its compare with bup or rsync.
some ppl have already started working on this and there's been activity on the mailing list lately about this topic.
however it's a dangerous feature to add in (backup tools should never screw up their storage, and this feature goes and removes things) so a lot of care is needed.
the boring answer is: it's coming, and we need a lot of help for vetting patches and testing them out.
git annex is for more than just backups. In particular, it lets you store files on multiple machines and retrieve them at will. This lets you do backups to e.g. S3, but it also lets you e.g. store your mp3 collection on your NAS and then easily copy some files to your laptop before leaving on a trip. Any changes you make while you're offline can be sync'ed back up when you come back online.
You can prune old files in git-annex [1], and it also supports encryption. git-annex deduplicates identical files, but unlike Attic &co, it does not have special handling of incremental changes to files; if you change a file, you have to re-upload it to the remote server.
git-annex is actively developed, and I've found the developer to be really friendly and helpful.
[1] You can prune the old files, but because the metadata history -- basically, the filename to hash mapping -- is stored in git, you can't prune that. In practice you'd need to have a pretty big repository with a high rate of change for this to matter.
Is there an easy way to have the backups encrypted at rest? That's a nice feature of Duplicity. I don't have to worry about someone hacking my backup server or borrowing my USB drive having access to my data.
currently bup doesn't implement encryption (since it's a pretty hard feature to get right and we do want to finish coding other key features -- like old backup removal -- before we get to that)
some ppl have reported using an encrypted storage backend like ecryptfs to store their bup repositories in. that option shouldn't be too hard to put together.
This seems like a fantastic tool, and I would love to try this out. And, it's free!
My personal obstacle in using a tool like bup is the back-up space. I could definitely use this for on-site/external storage devices, but I also like to keep online/cloud copies. I currently use CrashPlan for that which affords me unlimited space. If CrashPlan would let me use their cloud with bup, wow, I would switch in a heartbeat. Perhaps cloud backup tools could learn some tricks from bup.
It is really easy to set up what folders to backup and where, and I use it whenever a backup is simply take all files from X, do the rolling backups at Y, and done.
I can see how this would be theoretically possible in the same way I could see using `git filter-branch` to remove one or more commits from a code repository. But as it requires walking back up the tree to recalculate all of the commit hashes based on the new state of your files, I suspect it would be an extremely slow/expensive operation in bup's case. Someone who knows more about bup's internals can correct me if I'm wrong.
I've been using duply http://duply.net/ for a while. It is a simple frontend for duplicity http://duplicity.nongnu.org/.
I find it very easy to setup. It also provides encrypted backups trough GPG.
> That is a dataset which is already deduplicated via copy-on-write semantics (it was not using ZFS deduplication because you should basically never use ZFS deduplication).
"Basically never" is an overstatement, but it is true to the point of "Never unless you already know why I said 'basically never'"
It boils down to the fact that ZFS maintains a mapping from hashes to LBNs. This allows write-time deduplication (as opposed to a scrubber that runs periodically and retroactively deduplicates already written blocks). This is somewhat memory intensive though. For smaller ZFS pools you can get away with just having lots of RAM (and with or without dedupe ZFS performs better the more RAM you have). For larger ones, you can add a SSD to act as additional disk cache.
Note in this example that they were already showing 128GB of RAM for a 17TB pool; the L2ARC was to augment that. In general, ZFS was designed with a much higher RAM/Disk ratio than a workstation typically has.
I'm not an expert by any means, but the most cited reasons are that it requires a very big amount of ram, and it depends a lot (obviously) on the type of data.
This looks very interesting as a replacement for rdiff-backup. Hopefully the missing parts aren't too far away (expire old backups, restore from remote).
do you mean something that would automatically update the backup when a file is changed on disk?
bup currently doesn't do that. but there's been some talk of using inotify or another such method of knowing exactly which files are modified when they are so that bup could instantly work on those.
in theory it should be feasible, it's not implemented yet however
[+] [-] mappu|11 years ago|reply
Attic is one of the new-generation hash-backup tools (like obnam, zbackup, Vembu Hive etc). It provides encrypted incremental-forever (unlike duplicity, duplicati, rsnapshot, rdiff-backup, Ahsay etc) with no server-side processing and a convenient CLI interface, and it does let you prune old backups.
All other common tools seem to fail on one of the following points
- Incremental forever (bandwidth is expensive in a lot of countries)
- Untrusted remote storage (so i can hook it up to a dodgy lowendbox VPS)
- Optional: No server-side processing needed (so i can hook it up to S3 or Dropbox)
If your backup model is based on the old' original + diff(original, v1) + diff(v1, v2).. then you're going to have a slow time restoring. rdiff-backup gets this right by reversing the incremental chain. However, as soon as you need to consolidate incremental images, you lose the possibility of encrypting the data (since encrypt(diff()) is useless from a diff perspective).
But with a hash-based backup system? All restore points take constant time to restore.
Duplicity, Duplicati 1.x, and Ahsay 5 don't support incremental-forever. Ahsay 6 supports incremental-forever at the expense of requiring trust in the server (server-side decrypt to consolidate images). Duplicati 2 attempted to move to a hash-based system but they chose to use fixed block offsets rather than checksum-based offsets, so the incremental detection is inefficient after an insert point.
IMO Attic gets everything right. There's patches for windows support on their github. I wrote a munin plugin for it.
Disclaimer: I work in the SMB backup industry.
[+] [-] kijin|11 years ago|reply
If the original box is ever compromised, I don't want the attacker to gain any access to the backup. If you use a dumb storage like S3 as your backup server, you need to store your keys on the original box, and anyone who gains control of the original box can destroy your S3 bucket as well. Ditto for any SSH-based backup scheme that requires keys to be stored on the original box. A compromised box could also lie about checksums, silently corrupting your backups.
Backups should be pulled from the backup box, not pushed from the original box. Pushing backups is only acceptable for consumer devices, and even then, only because we don't have a reliable way to pull data from them (due to frequently changing IP addresses, NAT, etc).
The backup box needs to be even more trustworthy than the original box, not the other way around. I'm willing to live with a significant amount of overhead, both in storage and in bandwidth, in order not to violate this principle.
The backup box, of course, could push encrypted data to untrusted storage, such as S3. But only after it has pulled from the original box. In both cases, the connection is initiated from the backup box, not the other way around. The backup box never accepts any incoming connection.
Does Attic support this kind of use case? The documentation doesn't seem to have anything to say about backing up remote files to local repositories. I don't see any reason why it won't be supported (since rsync does), but "nominally supported" is different from "optimized for that use case", and I suspect that many of the latest generation of backup tools are optimized for the opposite use case.
[+] [-] rsync|11 years ago|reply
"Attic can initialize and access repositories on remote hosts if the host is accessible using SSH."
Fantastic. Will work perfectly here. We[1] are happy to support this just like we've supported duplicity all of these years. EDIT: appears obnam also works over plain old SSH. Can't tell about zbackup, however...
As always, email us to discuss the "HN Readers" discount.
[1] rsync.net
[+] [-] witten|11 years ago|reply
[1] https://attic-backup.org/quickstart.html#automating-backups [2] http://torsion.org/hg/atticmatic/file/tip [3] http://torsion.org/hg/atticmatic/file/tip/sample/config
[+] [-] StavrosK|11 years ago|reply
Here's a blog post about it:
http://www.stavros.io/posts/holy-grail-backups/
[+] [-] anarcat|11 years ago|reply
take it with a grain of salt, but i am surprised to say that attic is at least as fast as bup.
[+] [-] tenfingers|11 years ago|reply
[+] [-] anarcat|11 years ago|reply
i've been amazed to notice how all my files have atimes from july, when i stopped using rsync to make backups and switched to bup. :p
[+] [-] photoGrant|11 years ago|reply
Could you or someone explain why these fantastic sounding tools don't get a developed front-end? Or if they do why am I missing them?
The best solution I've found is ChronoSync.
[+] [-] sciurus|11 years ago|reply
[+] [-] williamstein|11 years ago|reply
Elsewhere in this discussion people not some shortcomings of bup, namely not having its own encryption and not having the ability to delete old backups. For my applications, lack of encryption isn't an issue, since I make the backups locally on a full-disk encrypted device and transmit them for longterm storage (to another full disk encrypted device) only with ssh. The lack of being able to easily delete old backups is also not an issue since (1) I don't want to delete them (I want a complete history), and (2) the approach to deduplication and compression in bup makes it extremely efficient space wise, and it doesn't get (noticeably) slower as the number of commits gets large; this is in contrast to ZFS, where performance can degrade dramatically if you make a large number of snapshots, or other much less space efficient approaches where you have to regularly delete backups or you run out of space.
In this discussion people also discuss ZFS and deduplication. With SageMathCloud, the filesystem all user projects use is a de-duplicated ZFS-on-Linux filesystem (most on an SSD), with lz4 compression and rolling snapshots (using zfssnap). This configuration works well in practice, since projects have limited quota so there's only a few hundred gigabytes of data (so far less than even 1TB), but the machines have quite a lot of RAM (50+GB) since they are configured for lots of mathematics computation, running IPython notebooks, etc.
[+] [-] tenfingers|11 years ago|reply
It's a great tool, but since you contributed already, I cannot understate the importance of pruning old archives. For online/disk-based backup solutions, space is always going to run out eventually.
I'm using bup where I already know the backup size will grow in a way that I can manage for the next 1-2 years.
For "classical" backup scenarios though, where binaries and many changes are involved and the backup grows by roughly 10-20% a week due to changes alone, I have to resort to tools where I can prune old archives because I would either have to reduce the number of increments (which I don't want to do) or increase the backup space by a factor of 50x (which I practically cannot do either).
[+] [-] rlpb|11 years ago|reply
Others have complained here that bup doesn't support deleting old backups. ddar doesn't have such an issue. Deleting snapshots work just fine (all other snapshots remain).
I think the underlying difference is that ddar uses sqlite to keep track of the chunks, whereas bup is tied to git's pack format, which isn't really geared towards large backups. git's pack files are expected to be rewritten, which works fine for code repositories but not for terabytes of data.
[+] [-] rakoo|11 years ago|reply
The real struggle of bup is how to know whether a hash is already stored, and how to know it screaming fast. It could be interesting to compare bup style and standard sqlite style, as you do in ddar.
Also, it seems ddar stores each object in its own file, like git loose objects. SQLite has a page [0] that compares this and storing blobs in SQLite, and I don't know what's the median size of your objects but if it's < 20k it seems to be better to just store them as blobs.
[0] https://www.sqlite.org/intern-v-extern-blob.html
[+] [-] femto|11 years ago|reply
Obnam, attic and similar use a normal read/write disk area, without any server side processing, so presumably an errant/malicious user is free to delete the entire backup?
[+] [-] Negitivefrags|11 years ago|reply
You can create a key that has write only access for your automated backups and a different key that has full access for administrative purposes.
That is what we do anyway.
[+] [-] rakoo|11 years ago|reply
[+] [-] beagle3|11 years ago|reply
However, bup goes one step farther and has builtin support for "par2" which adds error correction - in a way, it efficiently re-duplicates chunks so that whichever one (or two, or however many you decide) break, you can still recover the complete backup.
[+] [-] abcd_f|11 years ago|reply
[+] [-] derekp7|11 years ago|reply
The reason I ask, is I had a difficult time finding a backup tool that suited my own needs, so I wrote and open-sourced my own (http://www.snebu.com), and now that some people are starting to use it in production I'd like to get a deeper peer review to ensure quality and feature completeness. (I actually didn't think I'd be this nervous about people using any of my code, but backups are kind of critical so it I'd like to ensure it is done as correct as possible).
[+] [-] konradb|11 years ago|reply
[+] [-] uint32|11 years ago|reply
https://github.com/avdd/rsyncsync
Not polished, but it's working for me.
shell aliases showing how I use it are in my config repositoryencfs isn't ideal but it's the only thing that does the job. Ideally I'd use something that didn't leak so much, but it doesn't exist.
[+] [-] rsync|11 years ago|reply
https://raymii.org/s/articles/Set_up_your_own_truly_secure_e...
[+] [-] xorcist|11 years ago|reply
Obnam and bup seemed to work mostly the way I wanted to but obnam was by far the most mature tool, so this is what I chose in the end.
On the plus side, it provides both push and pull modes. Encryption and expiration works. The minus points are no Windows support, and some horror stories about performance. Apparently it can slow to a crawl with many files. I haven't run into that problem despite hundreds of gig in the backup set, but most are large files.
On the whole it's been very stable and unobtrusive during the time I've used it, but I haven't used it in anger yet. So a careful recommendation for obnam from me.
[+] [-] franole|11 years ago|reply
[1] http://mattmahoney.net/dc/zpaq.html
[+] [-] mynegation|11 years ago|reply
[+] [-] lelutin|11 years ago|reply
however it's a dangerous feature to add in (backup tools should never screw up their storage, and this feature goes and removes things) so a lot of care is needed.
the boring answer is: it's coming, and we need a lot of help for vetting patches and testing them out.
[+] [-] ars|11 years ago|reply
So they did the easy parts and skipped the hard parts.
Hardly a perfect backup.
I'm not sure a backup with all three of: delete old backups, encryption, and upload only differences even exists.
I think it might be one of those "pick any two" things, but if anyone knows of a backup with all three let me know.
[+] [-] unknown|11 years ago|reply
[deleted]
[+] [-] jlebar|11 years ago|reply
git annex is for more than just backups. In particular, it lets you store files on multiple machines and retrieve them at will. This lets you do backups to e.g. S3, but it also lets you e.g. store your mp3 collection on your NAS and then easily copy some files to your laptop before leaving on a trip. Any changes you make while you're offline can be sync'ed back up when you come back online.
You can prune old files in git-annex [1], and it also supports encryption. git-annex deduplicates identical files, but unlike Attic &co, it does not have special handling of incremental changes to files; if you change a file, you have to re-upload it to the remote server.
git-annex is actively developed, and I've found the developer to be really friendly and helpful.
[1] You can prune the old files, but because the metadata history -- basically, the filename to hash mapping -- is stored in git, you can't prune that. In practice you'd need to have a pretty big repository with a high rate of change for this to matter.
Edited for formatting.
[+] [-] glandium|11 years ago|reply
"git-annex is not a backup system."
[+] [-] eli|11 years ago|reply
[+] [-] lelutin|11 years ago|reply
some ppl have reported using an encrypted storage backend like ecryptfs to store their bup repositories in. that option shouldn't be too hard to put together.
[+] [-] keehun|11 years ago|reply
My personal obstacle in using a tool like bup is the back-up space. I could definitely use this for on-site/external storage devices, but I also like to keep online/cloud copies. I currently use CrashPlan for that which affords me unlimited space. If CrashPlan would let me use their cloud with bup, wow, I would switch in a heartbeat. Perhaps cloud backup tools could learn some tricks from bup.
[+] [-] cpach|11 years ago|reply
[+] [-] zanny|11 years ago|reply
It is really easy to set up what folders to backup and where, and I use it whenever a backup is simply take all files from X, do the rolling backups at Y, and done.
[+] [-] rcthompson|11 years ago|reply
The one most likely to be a showstopper seems to be: "bup currently has no way to prune old backups."
[+] [-] Smudge|11 years ago|reply
[+] [-] labianchin|11 years ago|reply
[+] [-] konradb|11 years ago|reply
Looking at http://burp.grke.org/burp2/08results1.html it seems it can outperform Bup in some situations.
[+] [-] fragmede|11 years ago|reply
Can someone more experienced with ZFS say why?
[+] [-] aidenn0|11 years ago|reply
It boils down to the fact that ZFS maintains a mapping from hashes to LBNs. This allows write-time deduplication (as opposed to a scrubber that runs periodically and retroactively deduplicates already written blocks). This is somewhat memory intensive though. For smaller ZFS pools you can get away with just having lots of RAM (and with or without dedupe ZFS performs better the more RAM you have). For larger ones, you can add a SSD to act as additional disk cache.
Here's a quick description of that setup:
https://blogs.oracle.com/brendan/entry/test
Note in this example that they were already showing 128GB of RAM for a 17TB pool; the L2ARC was to augment that. In general, ZFS was designed with a much higher RAM/Disk ratio than a workstation typically has.
[+] [-] mgbmtl|11 years ago|reply
[+] [-] 0x0|11 years ago|reply
[+] [-] jshb|11 years ago|reply
[+] [-] lelutin|11 years ago|reply
bup currently doesn't do that. but there's been some talk of using inotify or another such method of knowing exactly which files are modified when they are so that bup could instantly work on those.
in theory it should be feasible, it's not implemented yet however