IDE vs SCSI drives

[sinck@ugive.com]

\_ [root@saguaro kev]# /sbin/hdparm -tT /dev/sda /dev/hde /dev/md0
\_ 
\_ /dev/sda:
\_  Timing buffer-cache reads:   128 MB in  1.02 seconds =125.49 MB/sec
\_  Timing buffered disk reads:  64 MB in  5.05 seconds = 12.67 MB/sec
\_ 
\_ /dev/hde:
\_  Timing buffer-cache reads:   128 MB in  1.03 seconds =124.27 MB/sec
\_  Timing buffered disk reads:  64 MB in  2.64 seconds = 24.24 MB/sec
\_ 
\_ /dev/md0:
\_  Timing buffer-cache reads:   128 MB in  0.90 seconds =142.22 MB/sec
\_  Timing buffered disk reads:  64 MB in  2.69 seconds = 23.79 MB/sec
\_ 
\_ (I've run this test a number of times and there's not much variation
\_ in the results.)
\_ 
\_ According to the hdparm manpage, the buffer-cache read numbers are
\_ "essentially an indication of the throughput of the processor, cache,
\_ and memory of the system under test."  I don't know why the number was
\_ so much higher for the md device.  (This is the RAID-1 device which
\_ represents the mirrored /dev/hde5 and /dev/hdg5 partitions.)

IIRC, the RAID howto mentions that READs can be faster on a RAID1
because it just has to wait for the first disk to respond.  So,
depending on magic hardware differences, you'll get slightly better
performance from that.

\_ The SCSI disk averaged 7.592 seconds to do the copy.  The IDE disk(s)
\_ averaged 4.3820 seconds.  Remember that for the latter operation, the
\_ OS has to write to *both* disks which form the mirror.  This comes out
\_ to 8.43 MB/sec for my SCSI disk and 14.61 MB/sec for the IDE disk
\_ array.  (I should try to find a way to write to just one disk to see
\_ how much performance the RAID-1 is costing me.)

De RAID one of the partitions...

\_ SCSI subsystem driver Revision: 1.00
\_ (scsi0) <Adaptec AIC-7890/1 Ultra2 SCSI host adapter> found at PCI 0/14/0
\_ (scsi0) Wide Channel, SCSI ID=7, 32/255 SCBs
\_ (scsi0) Downloading sequencer code... 392 instructions downloaded
\_ scsi0 : Adaptec AHA274x/284x/294x (EISA/VLB/PCI-Fast SCSI) 5.2.1/5.2.0
\_        <Adaptec AIC-7890/1 Ultra2 SCSI host adapter>
\_   Vendor: HP        Model: C6270A            Rev: 3846
\_   Type:   Processor                          ANSI SCSI revision: 02
\_ (scsi0:0:6:0) Synchronous at 80.0 Mbyte/sec, offset 31.
\_   Vendor: QUANTUM   Model: QM318000TD-SW     Rev: N491
\_   Type:   Direct-Access                      ANSI SCSI revision: 02
\_ 
\_ Note the 80.0 Mbyte/sec line.  

Perhaps the synchronous part?  It's been a while, but isn't there an
async mode?  Would that be wise?

\_ Comments?  In particular, I'd like those SCSI advocates to speak up
\_ and let me know what I'm doing wrong with my SCSI drive.  (I'd hate to
\_ think that I've been paying more money all of these years for less
\_ performance.)

Could it be that your SCSI drive itself isn't pumping at full rate?
Like a 5400 RPM drive is prolly going to be slower than a 7200 or 10k
drive...?

I also think part of the advantage of SCSI is multiple devices on the
same controller, not a 1-1 pairing.

David