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Re: Pathetic SATA performance

On Thu, Feb 01, 2007 at 08:34:20PM -0000, Pete Clarke wrote:
> Hi there,
> I have a file server, running Etch, with the following specs:
> P4, 1.7Ghz
> 512MB Ram
> 2 x SI based SATA I controllers
> 4 x Maxtor 250GB SATA drives
> It is set up with software RAID 5, and the overall performance is terrible.
> Every time it reboots (which happens due to dodgy power!), it does a RAID 
> resync, this takes up 90% CPU time (for md0_resync process) for 50 hours!!
> During this time, ANY access to the drive is painful.
> Now, I expected software RAID 5 to be slow, but not this bad - this is the 
> reading from hdparm:
> bungo:~# hdparm -tT /dev/md0
> /dev/md0:
> Timing cached reads:     2 MB in  4.71 seconds = 435.05 kB/sec
> Timing buffered disk reads:    8 MB in  3.13 seconds =   2.56 MB/sec
> Bad eh?
> Becuase they're SATA drives, hdparm cannot tune them - or indeed read their 
> current settings. Is there any way I can speed this beast up, if not I am 
> going to go back to my old PPro200-based file server, running SCSI->FCAL 
> bridge.

Wow, that is awful.

I dont' do raid5 since I only have two disks.  

Two identical Seagate Barracuda 7200 80 GB SATA drives (with the SATA I
rate limiting jumper removed), on my Asus MB nVidia chipset SATA-II
ports.  Each drive has three partitions, to for raid1, one for LVM.

hdparm -tT /dev/md0

Timing cached reads:    2424 MB in 2.00 seconds = 1212.23 MB/sec
Timing buffered disk reads:	62 MB in 0.84 seconds = 73.44 MB/sec.

What happens if you time the raw drives instead of md0?  For me on raid1,
its basically the same.  I'm wondering if one or more of your drives are
in difficulty and its slowing down the whole array.

What does smartmontools say about the drive's S.M.A.R.T.s?


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