[CoolCold]

> Figure 9: Durable writes with io_uring. Left: Writes and fsync are issued via io_uring or manually linked in the application. Right: Enterprise SSDs do not require fsync after writes.

This sounds strange to me, of not requiring fsync. I may be wrong, but if it was meant that Enterprise SSDs have buffers and power-failure safety modes which works fine without explicit fsync, I think it's too optimistic view here.

[ComputerGuru]

I suspect it’s a misunderstanding. PLP capacitors let the drive not flush writes before reporting a write completed in response to a sync request, but they don’t let the software skip making that call.

[jclulow]

Yeah that's just flat out not correct. If you're writing through a file system or the buffer cache and you don't fsync, there is no guarantee your data will still be there after, say, a power loss or a system panic. There's no guarantee it's even been passed to the device at all when an asynchronous write returns.

[mjasny]

Yes, for file systems these statements are true.

However, in our experiments (including Figure 9), we bypass the page cache and issue writes using O_DIRECT to the block device. In this configuration, write completion reflects device-level persistence. For consumer SSDs without PLP, completions do not imply durability and a flush is still required.

> "When an SSD has Power-Loss Protection (PLP) -- for example, a supercapacitor that backs the write-back cache -- then the device's internal write-back cache contents are guaranteed durable even if power is lost. Because of this guarantee, the storage controller does not need to flush the cache to media in a strict ordering or slow way just to make data persistent." (Won et al., FAST 2018) https://www.usenix.org/system/files/conference/fast18/fast18...

We will make this more explicit in the next revision. Thanks.