alt Hacker NewsYeah 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.
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.