[Users] discard support for SSD in OpenVZ kernel

Kirill Korotaev dev at parallels.com
Thu Aug 29 00:53:59 EDT 2013


I also want to add that SSD models referred to in  the bug (like OCZ one) are not server grade and you guys risk very much loosing your data or corrupting file system on power failure.
You should test it heavily.

On Aug 29, 2013, at 03:52 , Kir Kolyshkin <kir at openvz.org> wrote:

> On 08/28/2013 06:34 AM, spameden wrote:
>> 
>> 
>> 
>> 2013/8/28 Kir Kolyshkin <kir at openvz.org>
>> On 08/27/2013 08:20 AM, spameden wrote:
>>> ArchLinux wiki says:
>>> Warning: Users need to be certain that kernel version 2.6.33 or above is being used AND that their SSD supports TRIM before attempting to mount a partition with the discard flag. Data loss can occur otherwise!
>>> 
>>> So I guess it's not in the OpenVZ kernel?
>>> 
>>> I'd like to use TRIM because it increases performance to SSD drastically!
>> 
>> You'd better check it with Red Hat, looking into their RHEL6 documentation.
>> 
>> My quick googling for "rhel6 kernel ssd discard" shows that rhel6 kernel
>> do support trim, they have backported it (as well as tons of other stuff,
>> so this is hardly 2.6.32 kernel anymore).
>> 
>> I've just tested via hdparm (ofc it's not a perfect tool to test out disk performance but still), here is what I get on the latest 2.6.32-042stab079.5:
>> 
>> # hdparm -t /dev/mapper/vg-root
>> /dev/mapper/vg-root:
>>  Timing buffered disk reads: 828 MB in  3.00 seconds = 275.56 MB/sec
>> 
>> on standard debian-7 kernel (3.2.0-4-amd64):
>> # hdparm -t /dev/mapper/vg-root
>> /dev/mapper/vg-root:
>>  Timing buffered disk reads: 1144 MB in  3.00 seconds = 381.15 MB/sec
>> 
>> and it's only read speed test.
>> 
>> I don't get why it differs so much?
>> 
> 
> My suggestion is, since this functionality is not directly related to OpenVZ, and
> we usually don't change anything in this code (unless there is a reason to), to
> try reproducing it on a stock RHEL6 kernel and, if it is reproducible, file a bug
> to red hat or, if it's not reproducible, file a bug to openvz.
> 
> Kir.
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> Users at openvz.org
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