Re: RAID5 TRIM/DISCARD user land support (fstriim and mkfs)

[Holger Kiehl <Holger.Kiehl@dwd.de>]

Hello,

On Mon, 10 Aug 2015, Christian Balzer wrote:

>
> Hello,
>
> Debian system, tested both Wheezy and Jessie, thus 3.16 kernel with
> backports.
>
> 8 SSD RAID5, of course with raid456.devices_handle_discard_safely set to 1.
> I can re-mount it with discard w/o a problem:
> ---
> EXT4-fs (md4): re-mounted. Opts: stripe=112,data=ordered,discard
> ---
>
> However fstrim whines about "FITRIM ioctl failed: Operation not supported"
> and mkfs.ext4 unsurprisingly doesn't discard things when invoked.
>
> The same HW/OS combo works fine with RAID10.
>
> When looking at the sysfs entries for that MD device the fact
> that /sys/class/block/md4/queue/discard_zeroes_data is 0 doesn't instill
> me with hope or confidence
>
> Now while the SSDs in question (Intel DC S3610s) don't really need TRIM
> really would have liked them to be able to start with a clean slate so to
> speak.
>
> Any insights?
>
Discard for raid456 has been disabled by default because some devices in
some cases don't do what it says on the label.

You can enable it by setting the module parameter

    raid456.devices_handle_discard_safely=Y

Ensure that your drives can handle discard safely.

Regards,
Holger