I've got two internal 135GB SAS drives in a RAID 0 array making a 270GB logical volume talking to my Dell Precission T5500 motherboard via a Dell supplied SAS 6iR controller.
I SaveAs an 480MB Excel 2003 file into a new filename.
Using Performance Monitor I can see that the peak Disk Write is 31MB/sec. Mmmm... looks a bit slow...
SaveAs the same file to an external 2TB 7.2krpm SATA drive (SATA III drive inside a SATA II caddy) talking to the MB through its eSATA port and I get peak Disk Write of 100MB/s making the operation considerably quicker.
That's right two SAS 15krpm RAID 0 drives write at 31MB/s and a single 7.2rpm SATA (SATA II effectively) external drive writes at 100MB/s. WTF!!!
Does this indicate:
- a problem with my SAS drives
- a very poor SAS 6iR controller
- Something else?
Admitedly the RAID 0 volume only has 59GB free out of its 270GB Total, and although the disk is defraged once a week maybe the free space is all in the inner sectors, whereas the external drive is pretty much empty and maybe it's writing to its outer sectors, but still this can't account for the massive difference, or can it?
The story isn't as bad here
loading up said 480MB file into Excel 2003.
Peak Disk Read of the SAS RAID 0 array is 220MB/sec.
Loading from the external SATA drive i get a peak of 96MB/sec
So assuming RAID 0 should read about twice as fast as a single drive, I am getting 220/(96*2)-1 = 14% performance improvement from SAS 15krpm drives vs SATA II 7.2krpm drives. This is disapointing to say the least.
Is there something possibly wrong in my setup?
It is possibly note worthy that the SATA drive reads and writes at about the same speed of 100MB/sec, whereas the SAS RAID 0 array reads at 220MB/s but writes at 31MB/s. That's a write speed of 14% of the read speed...
The problem seems to be with the SAS drives. I have swaped the 15k rpm SAS drives for two new SATA III 7.2k rpm drives, used them to build a new RAID 0 array off the same controller, dumped my Vista 64 OS onto it from an image I just made and now I am getting 220MB/s for both read and write. This is a x2.2 improvement over what I was getting with one of these SATA drives connected to the eSATA port which is what I was expecting on an internal SATA RAID 0.
I don't like downloading software from the net (security) but from the picture on the HDTune web page it looks like the drive on that test performs twice as fast on the outer sectors than on the inner sectors. Is that pretty much standard for all HDDs?
If so it is plausible that the 15k rpm SAS drives, being 78% full, are performing at 75% of their full speed (just reading the blue plot on the HDTune webpage), and this still gives 220MB/s reads, implying a 290MB/sec top speed, which would make them faster than the SATA drives and possibly the world makes sense again.
However the question remains why would I be getting a 31MB/s write speed if I can read at 220MB/s?
Edit3 : 2 April 2013 15:53
Believe it or not I still haven't received my two new matching SAS drives so I can re test (received two unmatched drives so had to send back and waiting...). When I have the new setup up and running I'll post to share the results