IDE vs SCSI drives

[Craig White]

Perhaps someone will clue me in to what IIRC actually means.

My first thought was that you are comparing new IDE drive technology to 4
year old SCSI technology. SOA of SCSI is ultra3 (160mbs) and ultra
controller like the Adaptec 29160 and 10,000 - 15,000 WD ultra3 drive would
probably dust the IDE's but you surely caught my attention with your post.
Then there are hardware RAID controllers that should really optimize
performance.

Also I don't seem to get the same reliability from IDE on servers that I get
from SCSI - however most of my firsthand comes from Windows NT which seems
to pretty well thrash an IDE drive in a years time.

Craig

> -----Original Message-----
> From: plug-discuss-admin@lists.plug.phoenix.az.us
> [mailto:plug-discuss-admin@lists.plug.phoenix.az.us]On Behalf Of
> sinck@ugive.com
> Sent: Wednesday, October 18, 2000 9:11 AM
> To: plug-discuss@lists.plug.phoenix.az.us
> Subject: IDE vs SCSI drives
>
>
>
> \_ [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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