Linux I/O schedulers - CFQ & random seeks

Hi Guys,

I'm in the process of setting up some new hardware and am just doing some basic disk performance testing with bonnie++
tostart with. 

I'm seeing a massive difference on the random seeks test, with CFQ not performing very well as far as I can see.  The
thingis I didn't see this sort of massive divide when doing tests with our current hardware. 

Current hardware: 2x4core E5420 @2.5Ghz/ 32GB RAM/ Adaptec 5805Z w' 512Mb/ Raid 10/ 8 15k 3.5 Disks
New hardware: 4x8core X7550 @2.0Ghz/ 128GB RAM/ H700 w' 1GB/ Raid 10/ 12 15.2k 2.5 Disks

Admittedly, my testing on our current hardware was on 2.6.26 and on the new hardware it's on 2.6.32 - I think I'm going
tohave to check the current hardware on the older kernel too. 

I'm wondering (and this may be a can of worms) what peoples opinions are on these schedulers?  I'm going to have to do
somereal world testing myself with postgresql too, but initially was thinking of switching from our current CFQ back to
deadline.

Any opinions  would be appreciated.

Regardless, here are some sample results from the new hardware:

CFQ:

Version  1.96       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
Way5ax      258376M   666  99 434709  96 225498  35  2840  69 952115  76 556.2   3
Latency             12344us     619ms     522ms     255ms     425ms     529ms
Version  1.96       ------Sequential Create------ --------Random Create--------
Way5ax              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 28808  41 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency              6170us     594us     633us    7619us      20us      36us

1.96,1.96,Way5ax,1,1299173113,258376M,,666,99,434709,96,225498,35,2840,69,952115,76,556.2,3,16,,,,,28808,41,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,12344us,619ms,522ms,255ms,425ms,529ms,6170us,594us,633us,7619us,20us,36us

deadline:

Version  1.96       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
Way5ax      258376M   696  99 449914  96 287010  47  2952  69 989527  78  2304  19
Latency             11939us     856ms     570ms     174ms     228ms   24744us
Version  1.96       ------Sequential Create------ --------Random Create--------
Way5ax              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 31338  45 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency              5605us     605us     627us    6590us      19us      38us

1.96,1.96,Way5ax,1,1299237441,258376M,,696,99,449914,96,287010,47,2952,69,989527,78,2304,19,16,,,,,31338,45,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,11939us,856ms,570ms,174ms,228ms,24744us,5605us,605us,627us,6590us,19us,38us

no-op:

Version  1.96       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
Way5ax      258376M   706  99 451578  95 303351  49  4104  96 1003688  78  2294  19
Latency             11538us     530ms    1460ms   12141us     350ms   22969us
Version  1.96       ------Sequential Create------ --------Random Create--------
Way5ax              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 31137  44 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency              5918us     597us     627us    5039us      17us      36us

1.96,1.96,Way5ax,1,1299245225,258376M,,706,99,451578,95,303351,49,4104,96,1003688,78,2294,19,16,,,,,31137,44,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,11538us,530ms,1460ms,12141us,350ms,22969us,5918us,597us,627us,5039us,17us,36us

--
Glyn