What am I doing wrong ??? Or is Adaptec 21610SA just a crappy RAID card ?

"J. Clarke" wrote in message
Toomas Soome wrote:
Tim Boyer wrote:

In about six months, I'm going to be in the market for a 2TB system, and
will have to make some of the same choices. Rita, _why_ is SCSI so much
better than SATA?

current data transfer rates (lets not argue about possible future
numbers, I have some but never done research for them):

SATA: 150Mb/s (up to 1.5Gb/s?)

No. 150 MB/sec. 3 Gb/sec hardware is shipping, not that it has any
real-world relevance.

It has for concentrators/expanders/portmultipliers (whatever they call it).

All allocated to a single device. No drive on the market, SCSI or SATA,
is capable of sustained transfers at anything close to this rate, so it's
adequate for any purpose.

Not if that drive is 1 of 4 hanging off a concentrator in a RAID configuration.


SCSI: 320Mb/s

Shared among up to 15 devices.

To 4 actually for simultanious access.
15 can be physically attached but aren't expected to run simultaniously.

No clear advantage to SCSI here unless you give each device
a separate channel, which gets hugely expensive very quickly.

SAS: 3Gb/s (roadmap up to 12Gb/s)?

Again, though, shared.

Nope, unless we are talking of an expander.

And you're interchanging bits and bytes. That's about 300 MB/sec.

FC-AL: 2Gb/s (roadmap up to 10Gb/s ?)

Again, shared. And that's roughly 200 MB/sec when you allow for overhead.

reliability:
SCSI MTBF 1,200,000 hours, many SATA drives only run to 600,000 MTBF

This has nothing to do with SATA vs SCSI--look up the specs on WD Raptors
and you'll find that same 1,200,000 MTBF. If you want enterprise-class
storage get enterprise-class storage.

(http://searchstorage.techtarget.com/...294586,00.html)

and some real numbers as well regarding to reliability:

Deskstar 7K400, http://www.hitachigst.com/hdd/support/7k400/7k400.htm
Error rate (non-recoverable) 1 in 10E14
Start/stops (at 40° C) 50,000

Ultrastar 15K147 http://www.hitachigst.com/hdd/support/15k147/15k147.htm
Error rate (non-recoverable) 1 in 10E15
Start/stops (at 40° C) 50,000

And if you look at the Raptor you'll find again 1 in 10E15.

in general, SATA will not replace SCSI anytime "soon", high end SCSI
will still outperform SATA in many terms... but SATA does definitely
have it's place as well.

While this is true, it is not for any of the reasons you stated. SCSI
does have a few real advantages--there's a lot more in the way of
enterprise-class host adapters and array cabinets and the like available
for one thing. For another it allows _much_ longer cables. For a third,
for now the fastest SATA drives do not match the speed or capacity of
the fastest SCSI drives, and for 10K RPM SATA drives there's no second
source--that last is a marketing issue, not a technical one--there's no
reason that 15K RPM SATA drives can't be produced by multiple vendors,
it's just that so far they've decided not to.

Further, it's all rather far afield as the problem the OP is describing
isn't really addressed by any of this. His basic problem remains that he
got a substandard array controller.

toomas

"J. Clarke" wrote in message
flux wrote:
In article , Toomas Soome wrote:

current data transfer rates (lets not argue about possible future
numbers, I have some but never done research for them):

SATA: 150Mb/s (up to 1.5Gb/s?)
SCSI: 320Mb/s
SAS: 3Gb/s (roadmap up to 12Gb/s)?
FC-AL: 2Gb/s (roadmap up to 10Gb/s ?)

These numbers may also be irrelevant depending on how the data is being
accessed. If, for example, you are connected to a server over Ethernet,
even SATA is faster (taking the numbers at face value) than gigabit.

reliability:
SCSI MTBF 1,200,000 hours, many SATA drives only run to 600,000 MTBF
(http://searchstorage.techtarget.com/...sid5gci1001942 tax294586,00.html)

What do those numbers actually mean? 1,200,000 hours is 136 years.

So this number taken at face value is pretty silly because it's
essentially saying it won't be until sometime in 22nd century before
just first SCSI hard disk anywhere on Earth fails!

That's not the service life--it doesn't take wear into consideration.

Of course it does.

If you have say 140 drives then you should expect one failure every year
out of that 140.

Only if it runs 24/7 and the MTBF is based on 24/7 POH.


Even not taken these numbers at face value, who is going to buy SATA
drives and keep them for several years? As long as they last through the
warranty period, you can just buy new ones. They are, after all, very
cheap. And you can bet the next generation will be bigger, better,
faster (e.g, SATA II), and cheaper.

For enterprise storage replacing drives every two years would be very
costly.

The price of the drives is peanuts compared to the cost of downtime.

So you configure your system for minimal downtime based on redundancy,
not single drive MTBF.

have to make some of the same choices. Rita, _why_ is SCSI so much better
than
SATA?

Drives themselves are better, SATA interface is used for medium-class models,
while SCSI is for high-end ones.

SCSI supports disconnects (parallel work of several drives on the same cable)
and tagged queue (the drive is aware of the IO request queue and can reorder it
itself using the information like rotation and actuator positions accessible to
firmware but not accessible to the OS).

ATA support for these features is pathetic, and not supported yet in many OSes
like Windows.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation

http://www.storagecraft.com

Maxim S. Shatskih wrote:

have to make some of the same choices. Rita, _why_ is SCSI so much
better
than
SATA?

Drives themselves are better, SATA interface is used for medium-class
models, while SCSI is for high-end ones.

What specific features or characteristics the WD Raptors as "medium-class"?

SCSI supports disconnects (parallel work of several drives on the same
cable)

SATA supports one drive per cable, so how would this be useful with SATA?

and tagged queue (the drive is aware of the IO request queue and
can reorder it itself using the information like rotation and actuator
positions accessible to firmware but not accessible to the OS).

ATA support for these features is pathetic, and not supported yet in many
OSes like Windows.

I see. So what specific properties make SCSI command queuing superior to
both the command queuing methods available with SATA?


--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

In article ,
"Peter" wrote:

You are completely wrong (did you ever studied statistics?).

Reread what I wrote carefully, and you will see that is quite correct.

Yes, I did. You have said:
"So this number taken at face value is pretty silly because it's
essentially saying it won't be until sometime in 22nd century before
just first SCSI hard disk anywhere on Earth fails!"

No your understanding is NOT correct, MTBF number does not imply that!



No, you are still misunderstanding. I was *intentionally* reading it as
a literal value.

In article ,
Malcolm Weir wrote:

On Thu, 02 Dec 2004 07:13:57 GMT, flux wrote:

In article ,
"J. Clarke" wrote:

For enterprise storage replacing drives every two years would be very
costly. The price of the drives is peanuts compared to the cost of
downtime.

This seems to imply nobody ever buys new equipment.

No, it doesn't. It implies that enterprises would rather replace
drives every three years, not every two, and would rather replace them
every four years than every three, etc.

How is three years any signficantly less costly than two?

In article ,
Malcolm Weir wrote:

Now, has it dawned on you that even the most rudimentary of network
servers has multiple NICs? Why do you think that is? Are server
manufacturers silly?

That's a very recent developlment. Even gigabit is relatively recent.

I strongly suspect that all your experience has been with the trivial
case, where you have (at most) a few file-sharing clients on a
network. In these case, you are right. But there's no money in that
market, since any fool can build such a system.

What other market is there?

Where *hard* problems are, at least for those of us in
comp.arch.storage, it is assumed that the network problem is already
solved. Need 10GB/sec of network bandwidth and don't have a 10G
Ethernet? Simply trunk 10 1000BaseT nets to your switch! Cisco (and
the like) can handle that part of the problem.

Again, this sounds very rare. Where are there disks fast enough to
saturate this much Ethernet?

In article ,
"Nik Simpson" wrote:

But they are basing their warranty calculations on how the drive is used,
and (with the exception of WD's 10K drives) they expect them to go into PC
devices which don't run 24x7, so the MTBF is expected to be stretched
because the drive is spending a good deal of its time doing very little or
powered down.

The Tivo I have attached to my TV streams video to disk 24/7. That's a
consumer appliance!

In an ordinary office environment, how would backups get accomplished if
the computers are running 24/7?

In article ,
Malcolm Weir wrote:

Ask any marketing professional about "take up" rates. For any offer,
service, or program that a manufacturer provides, some proportion of
customers won't take advantage of it even when they could. Sometimes
this is because they lose necessary documentation, other times because
they forget, and still more because they don't care about replacing
the failed unit with another equivalent unit (e.g. if you're going
through the hassle of replacing the thing, why not upgrade at the same
time?)

Or it could simply be the case that the drives are more reliable than
you believe.

A logical rebuttal might be that manufacturers could offer lifetime
warranties on SCSI drives because they are just that durable, but a
warranty that long doesn't make sense from a marketing point of view
because the manufacturers do want their customers to upgrade eventually.

You call *that* "logical"?

yes.

Do you really believe that the same proportion of people take
manufacturers up on the warranty after (say) 3 years as do after 1
month?

No, they probably upgrade. But wait didn't someone just say the cost of
upgrading is peanuts compared to the cost of downtime.

Yes, I did. You have said:
"So this number taken at face value is pretty silly because it's
essentially saying it won't be until sometime in 22nd century before
just first SCSI hard disk anywhere on Earth fails!"

No your understanding is NOT correct, MTBF number does not imply that!



No, you are still misunderstanding. I was *intentionally* reading it as
a literal value.

I don't think you will get anywhere with that sort of interpretation.