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

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

On Mon, 10 Aug 2015, Christian Balzer wrote:

> On Mon, 10 Aug 2015 08:28:39 +0000 (UTC) Holger Kiehl wrote:
>
>> 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
>>
> That's what I said I did in the 2nd sentence up there.
>
> If it were unset, a kernel warning
> "md/raid456: discard support disabled due to uncertainty."
> would be issued during RAID startup/assembly.
>
Rigth. Sorry, I did not read your mail properly.

Holger