Re: poor raid0 performance in 2.6.16-rc1-mm2?

["J.A. Magallon" <jamagallon@able.es>]

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On Tue, 24 Jan 2006 18:27:53 -0500, Ed Sweetman <safemode@comcast.net> wrote:

> I'll have to reboot to double check that this is specific to the above 
> kernel version, but It seems something is either wrong with my 
> particular kernel config for raid0, or my raid0 is setup wrong.
> 
> my raid0 uses 64k chunk sizes on an ext3 fs that's 367GB large, (across 
> two identical sata disks on nforce4 chipset)
> 
> I have partitions on both drives of equal size (2 altogether) that are 
> outside of the raid0.  I dbenched those partitions, the raid0 device, 
> and libata pata devices i also have (same rpm, less cache, same company).  
> 
> pata disk : 403MB/sec
> sata disk 1: 446MB/sec
> raid0 : between 336MB/sec and 386MB/sec
> 

Uh ? I want some of those disks....
How are you measuring that ?

Some more real numbers.

A SATA raid5:
nada:~# lsscsi
[1:0:0:0]    disk    ATA      Maxtor 7Y250M0   YAR5  -       
[2:0:0:0]    disk    ATA      Maxtor 7Y250M0   YAR5  -       
[3:0:0:0]    disk    ATA      Maxtor 7Y250M0   YAR5  -       
[4:0:0:0]    disk    ATA      Maxtor 7Y250M0   YAR5  -       
[5:0:0:0]    disk    ATA      Maxtor 7Y250M0   YAR5  -       
[6:0:0:0]    disk    ATA      Maxtor 7Y250M0   YAR5  -       
[7:0:0:0]    disk    ATA      Maxtor 7Y250M0   YAR5  -
nada:~# hdparm -t /dev/sdb /dev/sdc

/dev/sdb:
 Timing buffered disk reads:  156 MB in  3.02 seconds =  51.70 MB/sec

/dev/sdc:
 Timing buffered disk reads:  154 MB in  3.02 seconds =  50.96 MB/sec

nada:~# hdparm -t /dev/md0

/dev/md0:
 Timing buffered disk reads:  148 MB in  3.01 seconds =  49.20 MB/sec

An SCSI raid0 one (160 and 320 mixed...)

annwn:~# hdparm -t /dev/sdc /dev/sdb

/dev/sdc:
 Timing buffered disk reads:  226 MB in  3.02 seconds =  74.72 MB/sec

/dev/sdb:
 Timing buffered disk reads:  122 MB in  3.00 seconds =  40.64 MB/sec

annwn:~# hdparm -t /dev/md0

/dev/md0:
 Timing buffered disk reads:  242 MB in  3.00 seconds =  80.62 MB/sec


> now the sata disks alone, get 446MB/sec, but the raid device that's 
> comprised of them is getting >60MB/sec less throughput. 
> 
> This difference is much more drastic when say only 1 process is used 
> with dbench,
> 
> sata disk 1: 230MB/sec
> raid0 : 96MB/sec
> 
> 
> Something definitely feels wrong with these numbers. 
> 
> All filesystems are ext3, on an athlon 64 x2 system, during each test no 
> other io was performed, there is no swap and no other cpu intensive 
> operations were going on. 
> 
> the filesystems were all created the same way, and all have the same 
> blocksizes and such.  All are mounted with default options too. 
> -
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--
J.A. Magallon <jamagallon()able!es>     \               Software is like sex:
werewolf!able!es                         \         It's better when it's free
Mandriva Linux release 2006.1 (Cooker) for i586
Linux 2.6.15-jam5 (gcc 4.0.2 (4.0.2-1mdk for Mandriva Linux release 2006.1))

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