Time-honoured problem : RHEL3 iowait performance

Brendan Heading brendanheading at clara.co.uk
Sun Feb 18 14:00:59 CST 2007


Aaron wrote:

> This is probably not a logistical option, but you might try creating a 
> non-lvm volume and test the performance on it using the same controller 
> and same model of disks and raid configuration.  I am just throwing that 
> out there in the event that you have enough channels/drive bays to do 
> this.  Should it work out, you could always rsync the data over to the 
> new volume.

I tried this and the results are quite profound; it appears that the 
local disk LVM disk area goes considerably slower than the local disk 
non-LVM version.

Does anyone know why this might be ?

=================================


Benchmark on non-LVM :


Version  1.03       ------Sequential Output------ --Sequential Input- 
--Random-
                     -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
               8000M 45668  99 63714  27 36474  11 31716  60 64267  12 
563.3   1
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP 
/sec %CP
                  16  2644  81 +++++ +++ +++++ +++  3294  99 +++++ +++ 
11586  99
 
,8000M,45668,99,63714,27,36474,11,31716,60,64267,12,563.3,1,16,2644,81,+++++,+++,+++++,+++,3294,99,+++++,+++,11586,99

Benchmark on LVM :

Version  1.03       ------Sequential Output------ --Sequential Input- 
--Random-
                     -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
               8000M 17912  40 15313  18 11997  18 18669  44 25876  17 
224.2   2
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP 
/sec %CP
                  16   947   4 22868  41  2931  12  1054   5 29121  33 
2101   7
 
,8000M,17912,40,15313,18,11997,18,18669,44,25876,17,224.2,2,16,947,4,22868,41,2931,12,1054,5,29121,33,2101,7



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