Re: [OT] SATA vs. SCSI
On Thursday 27 October 2005 20:59, Allan Wind wrote:
>On 2005-10-27T19:33:22-0400, Gene Heskett wrote:
>> Our first foray into using a scsi based commercial server resulted in
>> its getting converted to ata disks fairly rapidly as the scsi raid
>> lost a drive at 2 week intervals. A single big atapi/eide drive
>> turned out to be faster, and a heck of a lot more reliable.
>
>While I feel for you, it's not a good idea to make decisions based on a
>single installation. If you have disks dying every 2 weeks, something
>else was up. Heat would be my first guess. Seagate, I think, had a
>batch of bad SCSI drives recently.
This was back when scsi drives were 8GB max, so quite a bit of water has
passed by now.
>Sign up for an account on http://www.storagereview.com/ and check out
>the reliability survey.
>
>I have good luck with IBM (2 GB) and Fujitsu (32 GB) SCSI drives, and
>had a Quantum (9 GB) die on me.
Those 6 & 8GBers were Quantum/Seagates. And. FWIW, the terrabyte arrays?
About 120 days old, a pair of them with 1394B interfaces to the outside
world, scsi3-320 inside, very well cooled, have each had at least 1 drive
failure in that 120 days.
6 drives in the storage array for a panasonic postbox were fairly good, I
think we replaced 2 of them in about 8 years of 24/7 usage in our
production bay, so that wasn't too bad.
Everytime I've dealt with scsi here at home, I've been burnt by short life
except for the 1GB seagate hawks, they're hockey pucks, and one Maxtor
7120s (120MB) that after nearly 12 years, finally got to needing a slap in
the chops with my hand to get it started. But I could probably hook it
back up to my old coco3, give it a hit, and use it till the next shutdown.
No surface errors the last time I checked it.
But, generally speaking, we've bought into the scsi is better scene
several times because the vendor peddling the gear swore on a stack of
bibles it was the be-all and end-all of all our problems, and with the
exception of the postbox, scsi has been a fscking disaster in a situation
where if it sneezes, 75,000 people see it and 3 will send us emails. The
only problem we had using ide drives in the commercial servers seemed to
be related to an effect known in the audiotape world as multipass
erasure, where a spot would start to pixelize on air, and the only cure
was to go back to our archive we keep on cdroms (about 1500 of them now)
and re-write that spot. But I haven't seen that effect recently, so
maybe ide drives are getting better both at error corrections and at bad
block housekeeping. The point is that we can lose one of those 200GB
drives, run down to Circuit City and grab another, install it, and have
the days workload of commercials loaded onto it in about an hour, so we
haven't lost that much income if any since we can route the other server
and screw with the local upn feed a lot cheaper than we can sit in black
during local times for CBS. We've never turned a bad scsi drive around
from the warranty in less than 4 days, and that could be several tens of
thousands of dollars in time loss for us.
So we tend to go with A: what works, and B: what can be fixed the
quickest when it doesn't work. Scsi in our extended experience, has come
in a distant 2nd place in dependability, a near 2nd place in performance,
and a very distant 2nd place in controlling operating costs.
>> Ditto here at home, I gave up on scsi tape drives about 18 months ago
>> and bought a 200GB atapi/eide drive & setup amanda's virtual tapes on
>> it. It has so far, been about 100x more dependable than the scsi tape
>> ever was.
>
>The interface is probably the most reliable thing on a tape drive. Are
>you comparing the same drive, same brand but just different interfaces?
Nope, cause tape drives tend to only come in scsi. The only exceptions
I'm aware of would have been the Travan drives which were available in
either. But the drive itself was a piece of warping plastic crap with a
lifetime often measured in sub year divisions. We had 5 of them at one
time, and 3 years later I had the last one in my office linux box useing
it with amanda. When it started making 2 piece tapes out of $48 tapes,
it went thump in the bin, less than 4 years old. I understand there was
even a floppy interface on some of the lower quality stuff, which might
have worked except the drives were even worse trash than the Travans were.
>> Now we've gotten into the video server scene, again with the
>> recommended terrabyte raid, scsi3-320 or some such based with a 1394B
>> (800 megabits/second=100 megabytes) interface to the servers, and
>> again scsi is being a problem child with an occasional stutter while
>> playing and always a missed first word as it starts.
>
>1394B -- array --> scsi --> disk? How many disks? Just curious. I
>could not get 1394 to work with Linux, and has to use USB for an
>external disk for the enclosure that I picked up after much resarch.
I could be wrong, but I think that pair of boxes has 6 drives in each
one. The scsi3 card is on an internal pci-x bus, so that part should be
good.
>> Put the same program file on a single internal big atapi/eide drive
>> and the performance is 100% reading while writing so we put in 2
>> drives per server.
>
>If it works for you good, great, it's a cheaper solution. If you
>starting pounding if with multiple users, it may not such a good
>solution and you may need more than one spindle to handle the load. I
>read one of the postgresql lists that IDE drives apparently claim sync
>data immediately while SCSI drives are truthful. That makes a
>difference when you are concerned about data transactional data.
No doubt. But our uses are more like playing 1 or 2, 1 hour mpeged tv
shows, while simultainously recording, or copying in which is much
quicker, 1 or 2 newer tv shows, plus a random load thats pretty heavy
just before and during the news as the individual reporters upload their
packages for playback during the newscasts. But those are smallish,
rarely over 2 minutes worth of material per package. So that comes in
over a gigabit ethernet cable in just a few seconds each. But we do as
much or more news in a day as any station thats not an all news format,
something in the order of 3.5 + morning cut-ins hrs a day during the week.
>> able to find an rsync workalike that does both branches of the apple
>> filesystem so that we can fabricate a darned near realtime, live,
>> online, redundant backup in case one server chassis should upchuck
>> in the middle of a program playback.
>>
>> If anyone has a clue how we can simulate an rsync run between 2 dual
>> g5 servers at 5 minute intervals, we're all ears.
>
>Suggest you start a new thread on this.
>
>
>/Allan
--
Cheers, Gene
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