[Users] discard support for SSD in OpenVZ kernel

spameden spameden at gmail.com
Thu Aug 29 06:10:41 EDT 2013


2013/8/29 Kirill Korotaev <dev at parallels.com>

> SSDSC2CW240A3 == Intel 520. It's not server grade as well and though it
> behaves much much better then desktop SSDs - we still saw it's loosing
> commits on power failure. So beware that your database can corrupt or loose
> transactions.
> All server grade SSDs from Intel have "Enhanced power-loss data
> protection" feature in specs which implies capacitors on the board for
> saving data to NVRAM. It's 320, 710 and S3700 models.
> Intel S3700 is the best and fastest we ever saw among different models
> including non-Intel ones and this is what Parallels recommends in Parallels
> Cloud Storage.
>

Ofc it's not that good, but we can't offer right now to buy overpriced
hardware (for us, at least).

Our database is XtraDB and it's commiting every second.

Losing 1 second of transactions is not a problem for us.

However, slow speed with 2.6.32 openvz kernel is a problem. As you can see
there is a problem on this particular kernel.

I'll try to investigate more and report back.

>
>
>
> On Aug 29, 2013, at 13:20 , spameden <spameden at gmail.com>
>  wrote:
>
>
>
>
> 2013/8/29 Kirill Korotaev <dev at parallels.com>
>
>> 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.
>>
>
> Thanks for that.
>
> But we are not using OCZ (also know they are not reliable).
>
> The SSD in this server is INTEL SSDSC2CW240A3.
>
> I can't try the latest redhat kernel on this system, because after
> converting it to deb it seems to be not working.
>
> But I believe fix should be in 2.6.32-358.18.1.el6.centos.plus.x86_64.
>
>>
>> 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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>>
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