CERC RAID5 performance lower than everyone else

[Alessandro FAGLIA]

-------- Original Message  --------
Subject: Re: CERC RAID5 performance lower than everyone else
From: Paul M. Dyer <pmdyer at ctgcentral2.com>
To: linux-poweredge at dell.com
Date: Fri Jul 18 2008 23:20:16 GMT+0200 (ora legale Europa occidentale)

Hi list! I've been watching to this thread because I'm also a (not very 
happy) owner of such RAID card (three SATA disks attached in RAID5 
configuration).
> Try setting the read-ahead buffer.   I find that helps some.
>
> /sbin/blockdev --setra 8192 /dev/sda
>
> Otherwise, switch to RAID-0 and you will really see an improvement.  Keep a backup.
>   
Before issueing this command to my PE SC1420 (running Debian Etch), I 
ran #hdparm -tT /dev/sda. This is the output:
> /dev/sda:
>  Timing cached reads:   1936 MB in  2.00 seconds = 967.58 MB/sec
> HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate 
> ioctl for device
>  Timing buffered disk reads:  162 MB in  3.02 seconds =  53.57 MB/sec
> HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate 
> ioctl for device
I've read that this error (HDIO_DRIVE_CMD(null) (wait for flush 
complete) failed: Inappropriate ioctl for device) is due to the fact 
that the command is run against a IDE disk (but this is not the case).
So I ask: why this output?


Thanks.
-- Alessandro