Re: SSD - TRIM command

[Phillip Susi <psusi@cfl.rr.com>]

On 2/9/2011 11:19 AM, Eric D. Mudama wrote:
> For SATA devices, ATA8-ACS2 addresses this through Deterministic Read
> After Trim in the DATA SET MANAGEMENT command.  Devices can be
> indeterminate, determinate with a non-zero pattern (often all-ones) or
> determinate all-zero for sectors read after being trimmed.

IIRC, it was a word in the IDENTIFY response, not the DATA SET
MANAGEMENT command.

On 2/9/2011 11:28 AM, Scott E. Armitage wrote:
> Who sends this command? If md can assume that determinate mode is
> always set, then RAID 1 at least would remain consistent. For RAID 5,
> consistency of the parity information depends on the determinate
> pattern used and the number of disks. If you used determinate
> all-zero, then parity information would always be consistent, but this
> is probably not preferable since every TRIM command would incur an
> extra write for each bit in each page of the block.

The drive tells YOU how its trim behaves; you don't command it.

If the drive is deterministic and always returns zeros after TRIM, then
mdadm could pass the TRIM down and process it like a write of all zeros,
and recompute the parity.  If it isn't deterministic, then I don't think
there's anything you can do to handle TRIM requests.