J.A. Magallón wrote:
> On Wed, 18 Jul 2007 10:56:11 +0100, Rui Santos <[email protected]> wrote:
>
>
>> Hi,
>>
>> I'm getting a strange slow performance behavior on a recently installed
>> Server. Here are the details:
>>
>>
> ...
>
>> I can get a write throughput of 60 MB/sec on each HD by issuing the
>> command 'time `dd if=/dev/zero of=test.raw bs=4k count=$(( 1024 * 1024 /
>> 4 )); sync`'
>>
>>
> ...
>
>> The RAID device I'm testing on is /dev/md2. Now, by issuing the same
>> command 'dd if=/dev/zero of=test.raw bs=4k count=$(( 1024 * 1024 / 4 ));
>> sync`' on the raid device mount point, I get the following speeds:
>> With stripe_cache_size at default '265': 51 MB/sec
>> With stripe_cache_size at '8192': 73 MB/sec
>>
>>
>
> I know many people consider this stupid, but can you post some hdparm -tT
> data ?
>
Of course. Here's the output:
NewServer-RD:~ # hdparm -tT /dev/md2
/dev/md2:
Timing cached reads: 1738 MB in 2.00 seconds = 868.93 MB/sec
Timing buffered disk reads: 444 MB in 3.01 seconds = 147.69 MB/sec
NewServer-RD:~ # hdparm --direct -tT /dev/md2
/dev/md2:
Timing O_DIRECT cached reads: 290 MB in 2.01 seconds = 144.05 MB/sec
Timing O_DIRECT disk reads: 396 MB in 3.01 seconds = 131.75 MB/sec
> The culprit can be the filesystem+pagecache, the md driver or the disk
> driver, so I think trying just hdparm will show if the disk o md are
> going nuts...
>
> In my case, I have a box with 2 raids, one with SCSI disks and one with
> IDE ones.
>
> Some results:
>
> lsscsi:
> [0:0:0:0] disk IBM DDYS-T18350N S96H /dev/sda
> [2:0:0:0] disk SEAGATE ST336807LW 0C01 /dev/sdb
> [2:0:1:0] disk SEAGATE ST336807LW 0C01 /dev/sdc
> [2:0:2:0] disk SEAGATE ST336807LW 0C01 /dev/sdd
> [2:0:3:0] disk SEAGATE ST336807LW 0C01 /dev/sde
> [3:0:0:0] disk ATA ST3120022A 3.06 /dev/sdf
> [3:0:1:0] cd/dvd HL-DT-ST DVDRAM GSA-4040B A300 /dev/sr0
> [4:0:0:0] disk ATA ST3120022A 3.76 /dev/sdg
>
>
> /dev/md0:
> Version : 00.90.03
> Creation Time : Mon Jun 18 13:40:57 2007
> Raid Level : raid5
> Array Size : 107522304 (102.54 GiB 110.10 GB)
> Used Dev Size : 35840768 (34.18 GiB 36.70 GB)
> Raid Devices : 4
> Total Devices : 4
> Preferred Minor : 0
> Persistence : Superblock is persistent
>
> Update Time : Wed Jul 18 13:31:22 2007
> State : clean
> Active Devices : 4
> Working Devices : 4
> Failed Devices : 0
> Spare Devices : 0
>
> Layout : left-symmetric
> Chunk Size : 256K
>
> UUID : 51ad72a7:a4d20d15:0f3ea3a1:5ccb49a0
> Events : 0.2
>
> Number Major Minor RaidDevice State
> 0 8 17 0 active sync /dev/sdb1
> 1 8 33 1 active sync /dev/sdc1
> 2 8 49 2 active sync /dev/sdd1
> 3 8 65 3 active sync /dev/sde1
>
> This is, four scsi disks on a Adaptec U320, doing raid5:
>
> /dev/sdb:
> Timing cached reads: 904 MB in 2.00 seconds = 451.84 MB/sec
> Timing buffered disk reads: 228 MB in 3.00 seconds = 75.90 MB/sec
> /dev/sdc:
> Timing buffered disk reads: 226 MB in 3.01 seconds = 75.01 MB/sec
> /dev/sdd:
> Timing buffered disk reads: 228 MB in 3.00 seconds = 75.88 MB/sec
> /dev/sde:
> Timing buffered disk reads: 226 MB in 3.00 seconds = 75.31 MB/sec
>
> /dev/md0:
> Timing buffered disk reads: 562 MB in 3.01 seconds = 186.88 MB/sec
>
> Nearly 75x3 = 215 Mb/s. And this looks like a small regression, I remember
> to have seen 200Mb on this setup on previous kernels.
> Performance is like 186/215 = 86%.
>
> And /dev/md1, raid0 on 2 IDE disks:
>
> /dev/sdf:
> Timing buffered disk reads: 148 MB in 3.02 seconds = 48.93 MB/sec
> /dev/sdg:
> Timing buffered disk reads: 124 MB in 3.00 seconds = 41.33 MB/sec
>
> /dev/md1:
> Timing buffered disk reads: 204 MB in 3.01 seconds = 67.68 MB/sec
>
> Performance: 67 / 90 = 75%, more or less...not too good.
>
> Now that I read the hdparm man page, perhaps would be better to repeat
> the tests with hdparm --direct.
>
> --
> J.A. Magallon <jamagallon()ono!com> \ Software is like sex:
> \ It's better when it's free
> Mandriva Linux release 2008.0 (Cooker) for i586
> Linux 2.6.21-jam12 (gcc 4.2.1 20070704 (4.2.1-3mdv2008.0)) SMP PREEMPT
> 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
>
>
>
>
Thanks for your reply.
Rui Santos
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