Disk Performance Issues

Bill Moran wmoran at potentialtech.com
Tue Apr 22 18:29:26 PDT 2003

Josh Paetzel wrote:
> I've got a FreeBSD 4.8-STABLE system with a Maxtor 6L040J2 ATA/133 7200 RPM 
> IDE OS drive in it on a gigabtye GA-7VRXP motherboard.  I've also got a pair 
> of Western Digital WD800BB 7200 RPM ATA/100 drives in RAID 1 on an onboard 
> Promise 20276 ATA/133 RAID Controller.  
> atacontrol reports that all the drives are being properly probed:
> ===root at markx ('tty') /storage/os_isos -> atacontrol mode 0
> Master = UDMA133 
> Slave  = ???
> ===root at markx ('tty') /storage/os_isos -> atacontrol mode 1
> Master = PIO4 
> Slave  = PIO4
> ===root at markx ('tty') /storage/os_isos -> atacontrol mode 2
> Master = UDMA100 
> Slave  = ???
> ===root at markx ('tty') /storage/os_isos -> atacontrol mode 3
> Master = UDMA100 
> Slave  = ???
> My issue is that I'm seeing sustained transfer rates on 600-700 meg files in 
> the 5-6 Meg/second range...about 1/4 of what the drives are capable of.  Does 
> anyone have any advice on where to go from here in troubleshooting this issue?

You're reading the specs wrong.  That drive is not capable of sustained through-
put of 133mb/s.  According to the data sheet, it can only do 44mb/s sustained.
That seems to be about what you're getting.  The ATA133 interface will only
go at 133 until the drive's buffers fill up, then it has to slow down to match
the actual speed the drive can transfer data to/from the platters.  Some of the
higher-end SCSI drives are capable of sustained speeds that high, but I don't
know of any 7200 RPM drives that can touch it.  Maxtor makes a 15000 RPM drive
that can (purportedly) sustain 75megabytes/sec. (wow!)

Bill Moran
Potential Technologies

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