On Wed, Sep 23, 2026 at 6:28 PM David Laight <[email protected]> wrote:
> And you really better do 4k aligned 4k writes. > Otherwise performance and device lifetime are likely to suffer badly. Agreed. My point about the 512-byte logical/atomic unit was only about what the device guarantees, not about what I/O size should normally be used. In particular, I don't think the fact that a device reports 512-byte logical blocks is a reason to use 512-byte I/O. Filesystems and applications should still normally issue appropriately aligned 4K (or larger) I/O where that matches the device's characteristics. The distinction I was trying to make is between the device's I/O granularity/performance characteristics and its guaranteed atomic write unit. The former may well be 4K or larger even when the latter is only 512 bytes (or is not advertised at all). So I agree with your point, but I don't think it changes the argument about the dm-crypt sector-size limit: a 4096-byte dm-crypt encryption sector can already span multiple device-level atomic units, and the proposed change only increases the maximum size when explicitly requested. Thanks, Itai
