[Users] discard support for SSD in OpenVZ kernel

[Kir Kolyshkin]

On 08/28/2013 06:34 AM, spameden wrote:
>
>
>
> 2013/8/28 Kir Kolyshkin <kir at openvz.org <mailto: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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