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Re: mkfs options for a 16x hw raid5 and xfs (mostly large files)

To: Ralf Gross <Ralf-Lists@xxxxxxxxxxxx>
Subject: Re: mkfs options for a 16x hw raid5 and xfs (mostly large files)
From: Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>
Date: Mon, 24 Sep 2007 16:43:39 -0400 (EDT)
Cc: linux-xfs@xxxxxxxxxxx
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On Mon, 24 Sep 2007, Ralf Gross wrote:

Justin Piszcz schrieb:
A bit ot: will I waste space on the RAID device with a 256K chunk size
and small files? Or does this only depend on the block size of the fs
(4KB at the moment).

That's a good question, I believe its only respective of the filesystem
size, but will wait for someone to confirm, nice benchmarks!

I use a 1 MiB stripe myself as I found that to give the best performance.

256KB is the largest chunk size I can choose for a raid set. BTW: the HW-RAID
is an Overland Ultamus 4800.

The funny thing is, that performance (256KB chunks) is even better without
adding any sw/su option to the mkfs command.

mkfs.xfs  /dev/sdd1 -f

Sequential Reads
File  Blk   Num                   Avg      Maximum      Lat%     Lat%    CPU
Size  Size  Thr   Rate  (CPU%)  Latency    Latency      >2s      >10s    Eff
----- ----- ---  ------ ------ --------- -----------  -------- -------- -----
20000  4096    1  208.33 23.81%     0.055       49.55   0.00000  0.00000   875
20000  4096    2  199.48 43.72%     0.116      376.85   0.00000  0.00000   456

Random Reads
File  Blk   Num                   Avg      Maximum      Lat%     Lat%    CPU
Size  Size  Thr   Rate  (CPU%)  Latency    Latency      >2s      >10s    Eff
----- ----- ---  ------ ------ --------- -----------  -------- -------- -----
20000  4096    1    2.83 0.604%     4.131       38.81   0.00000  0.00000   469
20000  4096    2    4.53 1.700%     4.995       67.15   0.00000  0.00000   266

Sequential Writes
File  Blk   Num                   Avg      Maximum      Lat%     Lat%    CPU
Size  Size  Thr   Rate  (CPU%)  Latency    Latency      >2s      >10s    Eff
----- ----- ---  ------ ------ --------- -----------  -------- -------- -----
20000  4096    1  188.15 42.98%     0.047     7547.93   0.00027  0.00000   438
20000  4096    2  167.76 76.89%     0.100     7521.34   0.00078  0.00000   218

Random Writes
File  Blk   Num                   Avg      Maximum      Lat%     Lat%    CPU
Size  Size  Thr   Rate  (CPU%)  Latency    Latency      >2s      >10s    Eff
----- ----- ---  ------ ------ --------- -----------  -------- -------- -----
20000  4096    1    2.08 0.869%     0.016        0.13   0.00000  0.00000   239
20000  4096    2    1.80 1.501%     0.020        6.28   0.00000  0.00000   12


Ralf



I find that to be the case with SW RAID (defaults are best)

Although with 16 drives(?) that is awfully slow.

I have 6 SATA's I get 160-180 MiB/s raid5 and 250-280 MiB/s raid 0 (sw raid).

With 10 raptors I get ~450 MiB/s write and ~550-600 MiB/s read, again XFS+SW raid.

Justin.


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