[rbranson]

> For e-commerce workloads, the performance benefit of write-back mode isn’t worth the data integrity risk. Our customers depend on transactional consistency, and write-through mode ensures every write operation is safely committed to our replicated Ceph storage before the application considers it complete.

Unless the writer is always overwriting entire files at once blindly (doesn't read-then-write), consistency requires consistency reads AND writes. Even then, potential ordering issues creep in. It would be really interesting to hear how they deal with it.

[twotwotwo]

They mention it as a block device, and the diagram makes it look like there's one reader. If so, this seems like it has the same function as the page cache in RAM, just saving reads, and looks a lot like https://discord.com/blog/how-discord-supercharges-network-di... (which mentions dm-cache too).

If so, safe enough, though if they're going to do that, why stop at 512MB? The big win of Flash would be that you could go much bigger.