[Lustre-discuss] slow direct_io , slow journal .. in OST log

Lex lexluthor87 at gmail.com
Tue Jan 26 17:59:52 PST 2010


Hi all

I heard somewhere about oversubscribing issue related to ost thread, but i
just wonder why i calculated followed the function that i founded in the
manual ( *thread_number = RAM * CPU core / 128 MB* - do correct me if
there's something wrong with it, please ) , the oversubscribing warning is
still appears.

Maybe i have to choose my own value from trial and error, but is there any
explanation for this situation?

@Erik : could u please describe your bottleneck problem with journal device
for me ? as detail as better ?


On Tue, Jan 26, 2010 at 10:00 PM, Erik Froese <erik.froese at gmail.com> wrote:

> Sorry Lex I misread your email. I saw similar messages about my journal
> devices. The OST is an ext3+extra features filesystem. Each FS has an
> associated journal that CAN be on a separate device. Its supposed to speed
> up small file operations. Mine were oversubscribed and became a bottleneck.
>
> Erik
>
>
> On Mon, Jan 25, 2010 at 11:40 AM, Lex <lexluthor87 at gmail.com> wrote:
>
>> Sorry Erik if i'm rising such a "bad" question, could u tell me more about
>> OST journal device ? I even don't know what it is as well as haven't seen it
>> before, in the lustre manual.
>>
>> Best regards
>>
>>
>> On Mon, Jan 25, 2010 at 10:52 PM, Erik Froese <erik.froese at gmail.com>wrote:
>>
>>> Is each OST journals on its own physical disk? I've seen those messages
>>> when there isn't enough hardware dedicated to the journal device.
>>> Erik
>>>
>>> On Sun, Jan 24, 2010 at 11:43 PM, Aaron Knister <aaron.knister at gmail.com
>>> > wrote:
>>>
>>>> I don't necessarily think there's anything wrong with using drbd or
>>>> running it over gigabit ethernet. If you stop all I/O to the lustre
>>>> filesystem, what does an hdparm -t show on the sdc and drbd devices? Do you
>>>> have any performance numbers for the drbd or underlying raid devices?
>>>>
>>>> On Jan 24, 2010, at 11:17 PM, Lex wrote:
>>>>
>>>> Thank you for your fast reply, Aaron
>>>>
>>>> I'm using Giga Ethernet to synchronize data between to our fail-over
>>>> node. Is there something wrong ? Tell me, please
>>>>
>>>> On Mon, Jan 25, 2010 at 10:35 AM, Aaron Knister <
>>>> aaron.knister at gmail.com> wrote:
>>>>
>>>>> My best guess (and please correct me if I'm wrong) is that those
>>>>> messages are because the underlying block devices are slow to respond to i/o
>>>>> requests. It looks like you're using DRBD. What's your interconnect?
>>>>>
>>>>> On Jan 24, 2010, at 9:42 PM, Lex wrote:
>>>>>
>>>>> Hi list
>>>>>
>>>>> I have one OSS with hadware info like this :
>>>>>
>>>>> CPU Intel(R) xeon E5420 2.5 Ghz
>>>>> Chipset intel 5000P
>>>>> 8GB RAM
>>>>>
>>>>> With this OSS, we using 2 RAID-5 arrays as OSTs ( each has 4 x 1.5 TB
>>>>> hard drive with RAID controller adaptec 5805 )
>>>>>
>>>>> I worked quite smooth before, but, about 2 weeks ago, in
>>>>> /var/log/messages, i saw many warning ( i thought so)  like this:
>>>>>
>>>>> *Jan 25 08:41:23 OST6 kernel: Lustre:
>>>>> 9587:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 35s
>>>>> Jan 25 08:41:34 OST6 kernel: Lustre:
>>>>> 9608:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 41s
>>>>> Jan 25 08:41:34 OST6 kernel: Lustre:
>>>>> 9608:0:(filter_io_26.c:706:filter_commitrw_write()) Skipped 2 previous
>>>>> similar messages
>>>>> Jan 25 08:41:35 OST6 kernel: Lustre:
>>>>> 9645:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 43s
>>>>> Jan 25 08:58:10 OST6 kernel: Lustre:
>>>>> 9646:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 31s
>>>>> Jan 25 08:59:39 OST6 kernel: Lustre:
>>>>> 9609:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 30s
>>>>> Jan 25 09:01:05 OST6 kernel: Lustre:
>>>>> 9587:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 33s
>>>>> Jan 25 09:03:23 OST6 kernel: Lustre:
>>>>> 9633:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 32s
>>>>> Jan 25 09:11:25 OST6 kernel: Lustre:
>>>>> 9585:0:(filter_io_26.c:706:filter_commitrw_write()) lustre-OST0006: slow
>>>>> direct_io 36s*
>>>>>
>>>>> I googled around and found that it's because a problem with
>>>>> oss_num_threads and even though brought it down to 64 ( followed by the
>>>>> function i found in the 1.8 manual: thread_number = RAM * CPU core / 128 MB,
>>>>> its value is 256  )
>>>>>
>>>>> *options ost oss_num_threads=64*
>>>>>
>>>>> It still didn't help.
>>>>>
>>>>> I thought it was only the harmless warning but maybe wrong, our
>>>>> performance is goes down quite heavily ( it's maybe because of other reason,
>>>>> but for now, i am only doubting slow direct_io problem )
>>>>>
>>>>> iostat -m 1 1
>>>>> Linux 2.6.18-92.1.17.el5_lustre.1.8.0custom (OST6)      01/25/2010
>>>>>
>>>>> avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>>>>>            0.01    0.02    2.86   25.01    0.00   72.10
>>>>>
>>>>> Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
>>>>> sda               1.30         0.01         0.00      11386       3469
>>>>> sdb               1.30         0.01         0.00      11531       3469
>>>>> sdc             131.50        *12.40*         0.26   11793218
>>>>> 249934
>>>>> sdd             178.46        *18.00*         0.26   17124065
>>>>> 250334
>>>>> md2               3.33         0.02         0.00      22915       2634
>>>>> md1               0.00         0.00         0.00          0          0
>>>>> md0               0.00         0.00         0.00          0          0
>>>>> drbd3           480.10        *12.39*         0.26   11789047
>>>>> 249639
>>>>> drbd6           565.85        *14.89*         0.26   14168452
>>>>> 249211
>>>>>
>>>>>
>>>>> So, could anyone please tell me whether it's warning impact our system
>>>>> performance or not ? and if it does, give me solution or advice to resolve
>>>>> it, please
>>>>>
>>>>> Best regards
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>  _______________________________________________
>>>>> Lustre-discuss mailing list
>>>>> Lustre-discuss at lists.lustre.org
>>>>> http://lists.lustre.org/mailman/listinfo/lustre-discuss
>>>>>
>>>>>
>>>>>
>>>>
>>>>
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>>
>
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