\_ [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
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