From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Alfred von Campe
Yes, I was going to say this too, make sure the SATA settings in the BIOS are all set to SATA operation and not "legacy", then you should see /dev/sda and /dev/sdb and all DMA, IO size, NCQ and multiple sector settings will be properly negotiated at start-up.
I bit the bullet and rebooted my system. I couldn't find anything in the BIOS regarding this. However, while the system was down, I simply swapped the SATA connections of one of the optical drives with the slow hard disk. Upon reboot, the slow disk formerly at /dev/hda disk was now /dev/sda (and the former /dev/sda was now /dev/sdb) and the two optical drives are /dev/hda and /dev/hdb. Moreover, the disk drive now performs as before.
So why does a simple swap like this cause such a performance difference (almost an order of magnitude!)?
Well most desktop motherboards these days provide for 2 SATA devices and 2 emulated PATA devices. Though the emulated PATA devices will probably end up using PIO instead of DMA for transfers which is slow and processor intensive, so these are usually reserved for optical drives, which are slow.
I would still have the 2 optical drives hda/hdb set for DMA transfer too as watching DVDs will be choppy and burning CDs/DVDs may be fraught with failures.
You may want to set the multiple sector transfer too to what the drives support in their specs.
If all your devices are fully SATA compliant I would dig through the vendor docs for your motherboard to see if there is a non- intuitive option in the BIOS to set all connectors to SATA mode.
To set these via hdarpm:
hdparm -c 1 /dev/hda (for 32-bit) hdparm -d 1 /dev/hda (for DMA) hdparm -m 16 /dev/hda (multiple sector IO = 16 sectors)
These can be combined to: hdparm -c 1 -d 1 -m 16 /dev/hda
Now that the drive is /dev/sda, hdparm doesn't work. Is there a similar utility to change these settings on SATA drives that show up as /dev/sdx? Is this even needed? In my case, I'm happy to get back the previous performance, but if there is a way to increase it even further, I'd like to know.
Most cases this isn't needed, but if you want to view and access information on SATA/SAS/SCSI disks you can google for 'sdparm', but it isn't as user-friendly as hdparm and not all options are implemented for SATA drives as they support a limited SCSI command spec.
-Ross
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