Best [SCSI] disk performance in Linux
James Turner
Recently I have been considering doing an upgrade on my system,
focusing on improving disk speed (both throughput and latency). Right
now, I've got a fairly standard IDE setup (two hard drives, one two
years old, one three years old) on separate cables (and channels).
They are fine and work well, except for performance, which is why I am
considering an upgrade in the next few months.
Right now, I am looking at a Seagate Cheetah drive. Capacity is not
really as important as speed, so the 4.5gig looks to be what I will
get. Am I right in assuming this is the fastest SCSI drive for use
under Linux?
I have been reading old posts in Dejanews, and checking websites, and
it appears that the SCSI controller of choice would be a Bus Logic
BT-938 (forgive me if that's not the right model number, my notes are
elsewhere). I am looking for stability and speed. Initially I had
planned on an Adaptec 2940UW, but it would seem that the drivers in
Linux are not as stable nor as efficient as the Bus Logic (or the
Diamond Fireport, which I have also read good things about).
Roughly, my needs are as follows. I'm getting very much into Linux
development, and disk speed is definitely something I would like to
improve. Right now I'm running an AMD K6-200 with 128meg RAM, and a
fairly slow disk subsystem. I own a SCSI Zip drive (running through a
16bit ISA Future Domain controller). I would like to run both the
Cheetah and the Zip from the same card, as well as in the future
perhaps add a CD writer and/or a scanner.
Any thoughts on the best SCSI card (as well as a different disk if my
research in that area has gone wrong) would be greatly appreciated.
Also, would purchasing a kit or an OEM card be best? Am I right in
assuming that the OEM comes with no cables? Would it be cheaper just
to buy the cables I need?
Thanks in advance.
--
James Turner turn...@xtn.net
http://cswww.vuse.vanderbilt.edu/~turnerj1/
James Turner
Chris Mauritz <ri...@ritz.mordor.net> writes:
> > Right now, I am looking at a Seagate Cheetah drive. Capacity is not
> > really as important as speed, so the 4.5gig looks to be what I will
> > get. Am I right in assuming this is the fastest SCSI drive for use
> > under Linux?
>
> If you want speed, you'll get better performance if you use 2
> 7200rpm (hawk/barracuda/cheetah) drives and use the md driver
> to stripe them together (RAID 0). The Seagate Hawk 4.5gig
> drives (34555N?) are just under $300 these days so you could
> get two of those for less than the cost of a 4.5gig Cheetah and
> enjoy more capacity and better performance.
I experimented with md using my IDE drives and was somewhat
disappointed with the results. There wasn't any perceptable
throughput increase, yet there was a distinctive increase in latency.
I think the problem is simply that one of my disks is a fair bit
slower than the other (about 18 months).
md however seemed stable... except I had one crash, which is pretty
much unheard of on my box, and when something like a crash happens, I
know something odd is going on. I went back to regular partitioning
and haven't crashed since, though I have no other evidence md was a
problem.
(Okay, I have messed up a glibc install, and my system would kernel
panic on loading init, but that's what dd and a zip disk are
for... worked great. For anyone who likes to experiment and
occasionally cause boot problems, I highly suggest this. Before hand
I had dd'd my room parititon [80 meg or so] to the zip and it worked
wonderfully as a rescue disk, just added a root param to lilo).
I assume using SCSI disks of high wuality would definitely have better
results than my previous experiences. Are there any benchmark results
which indicate a true performance gain? And was my latency/seek
problem merely a result of one disk being faster than the other, or
was it a product of striping in general?
One thing I forgot to mention in my original post was regarding SCSI
backup systems. Are they worth the cost compared to cheaper (albeit
slower) floppy drives? What is the current status of support for such
devices under Linux, and is backup software very sophisticated (by
that I don't mean nice interfaces, I just mean reliable, efficient,
and well-suited for incremental/differential/daily backups). I
honestly don't know much about backups per-se, though I know I would
like to have the added peace of mind (not to mention since using RAID0
would slightly more than double the chances of losing data, since
there are two disks that can fail).
Again, thanks!
David Rees
James Turner wrote:
>
> I experimented with md using my IDE drives and was somewhat
> disappointed with the results. There wasn't any perceptable
> throughput increase, yet there was a distinctive increase in latency.
> I think the problem is simply that one of my disks is a fair bit
> slower than the other (about 18 months).
The problem isn't with your disks, but with the IDE interface, which
doesn't support parallel reads/writes. Basically, only one disk can do
anything at a time per channel. If you were to use equivalent SCSI
disks, on a controller which could handle the bandwidth, you'd get your
2X speedup.
-Dave
Chris Mauritz
James Turner <turn...@xtn.net> wrote:
> Recently I have been considering doing an upgrade on my system,
> focusing on improving disk speed (both throughput and latency). Right
> now, I've got a fairly standard IDE setup (two hard drives, one two
> years old, one three years old) on separate cables (and channels).
> They are fine and work well, except for performance, which is why I am
> considering an upgrade in the next few months.
> Right now, I am looking at a Seagate Cheetah drive. Capacity is not
> really as important as speed, so the 4.5gig looks to be what I will
> get. Am I right in assuming this is the fastest SCSI drive for use
> under Linux?
If you want speed, you'll get better performance if you use 2
7200rpm (hawk/barracuda/cheetah) drives and use the md driver
to stripe them together (RAID 0). The Seagate Hawk 4.5gig
drives (34555N?) are just under $300 these days so you could
get two of those for less than the cost of a 4.5gig Cheetah and
enjoy more capacity and better performance.
Regards,
C
--
Chris Mauritz | Network Security & Design
Network Engineer | 56k-T3 connectivity to the Net.
ri...@mordor.net <--fun biz--> | http://www.new-york.net/
Magnus Back
So where do we find md?
By the way cheetah is not 7200rpm.
It's 10000 rpm or something similar.
/// Magnus Back
In article <Eq72u...@news2.new-york.net>,
James Turner
David Rees <dr...@oto.dyn.ml.org> writes:
> > I experimented with md using my IDE drives and was somewhat
> > disappointed with the results. There wasn't any perceptable
> > throughput increase, yet there was a distinctive increase in latency.
> > I think the problem is simply that one of my disks is a fair bit
> > slower than the other (about 18 months).
>
> The problem isn't with your disks, but with the IDE interface, which
> doesn't support parallel reads/writes. Basically, only one disk can do
> anything at a time per channel. If you were to use equivalent SCSI
> disks, on a controller which could handle the bandwidth, you'd get your
> 2X speedup.
On the same channel, that is true, but I was using two different
channels and, as I understand it, the parallel problems don't exist.
My motherboard has two IDE ports (for 4 devices), and each port is a
different channel, so I slightly changed the hookup (originally both
hard drives were on channel 1, and a cdrom on channel two; I changed
this so each hard drive was on its own channel with the cd-rom on the
same channel as the slow disk).
On a related note, is there a proper way to measure disk throughput?
In my somewhat ad hoc experiments, I would "time dd if=/dev/hda
of=/dev/null bs=209715200 count=1" to read 200 megabytes from a disk,
and figure out throughput that way. It seems that this is a fairly
good way off-hand to measure streamed throughput, though I'm sure it
doesn't measure real-world throughput. Are there any existing
programs to measure throughput and latency in a Linux box? For that
matter, have there ever been any real-world comparisons on performance
for IO subsystems (ethernet and disk primarily) of identically
equipped Linux and Windows NT boxes? I'd be interested to know
particularly how much more efficient Linux is at disk access (if it is
more efficient, which I would assume so, but maybe I'm a bit biased
*grin*).
Thanks,
Chip
Chris Mauritz
James Turner <turn...@xtn.net> wrote:
> Chris Mauritz <ri...@ritz.mordor.net> writes:
>> > Right now, I am looking at a Seagate Cheetah drive. Capacity is not
>> > really as important as speed, so the 4.5gig looks to be what I will
>> > get. Am I right in assuming this is the fastest SCSI drive for use
>> > under Linux?
>>
>> If you want speed, you'll get better performance if you use 2
>> 7200rpm (hawk/barracuda/cheetah) drives and use the md driver
>> to stripe them together (RAID 0). The Seagate Hawk 4.5gig
>> drives (34555N?) are just under $300 these days so you could
>> get two of those for less than the cost of a 4.5gig Cheetah and
>> enjoy more capacity and better performance.
> I experimented with md using my IDE drives and was somewhat
> disappointed with the results. There wasn't any perceptable
> throughput increase, yet there was a distinctive increase in latency.
> I think the problem is simply that one of my disks is a fair bit
> slower than the other (about 18 months).
All bets are off with IDE. Yick.....
I suspect either one disk is substantially slower or your processor
doesn't have enough oomph to deal with all that programmed IO.
> md however seemed stable... except I had one crash, which is pretty
> much unheard of on my box, and when something like a crash happens, I
> know something odd is going on. I went back to regular partitioning
> and haven't crashed since, though I have no other evidence md was a
> problem.
I have been using the md driver 24x7 on 2 different linux boxes running
2 different motherboards with totally different disks and processors
and have yet to have a crash.
> (Okay, I have messed up a glibc install, and my system would kernel
> panic on loading init, but that's what dd and a zip disk are
> for... worked great. For anyone who likes to experiment and
> occasionally cause boot problems, I highly suggest this. Before hand
> I had dd'd my room parititon [80 meg or so] to the zip and it worked
> wonderfully as a rescue disk, just added a root param to lilo).
Perhaps you have some bogons still stuck in your binary tree somewhere?
It seems silly to blame the md driver for that.
> I assume using SCSI disks of high wuality would definitely have better
> results than my previous experiences. Are there any benchmark results
Yes.
> which indicate a true performance gain? And was my latency/seek
> problem merely a result of one disk being faster than the other, or
> was it a product of striping in general?
It has nothing to do with striping.
> One thing I forgot to mention in my original post was regarding SCSI
> backup systems. Are they worth the cost compared to cheaper (albeit
> slower) floppy drives? What is the current status of support for such
Yes. The floppy tape drives are a pretty useless solution both from
a speed perspective and from a cost of media perspective. If you
make frequent backups (why buy a tape if you're not, right?) it's
hard to beat the media cost of DAT ($6-7 for a 90 meter tape that
will hold 2-4gb of data). The floppy tape drives might be a solution
for you if you absolutely can't afford a SCSI tape and you make
infrequent backups.
Chris Mauritz
Magnus Back <Magnu...@gol.com> wrote:
> So where do we find md?
I forget where I got it. I believe at ftp.redhat.com/contrib
> By the way cheetah is not 7200rpm.
> It's 10000 rpm or something similar.
I'm aware of that. The other drives I was recommending are 7200rpm.
Regards,
Eric Lee Green
On 22 Mar 1998 08:32:30 -0500, James Turner <turn...@xtn.net> wrote:
>David Rees <dr...@oto.dyn.ml.org> writes:
>> The problem isn't with your disks, but with the IDE interface, which
>> doesn't support parallel reads/writes. Basically, only one disk can do
>> anything at a time per channel. If you were to use equivalent SCSI
>> disks, on a controller which could handle the bandwidth, you'd get your
>> 2X speedup.
>
>On the same channel, that is true, but I was using two different
>channels and, as I understand it, the parallel problems don't exist.
You understand wrong. By default, IDE drives operate in PIO mode,
i.e., every byte must be read "by hand" by the CPU. What ends up
happening is that I/O operations end up serialized -- the OS reads a
sector from one controller, then reads a sector from the next
controller, rather than both transfers happening semi-simultaneously
as with bus master DMA SCSI with disconnect capability (which allows
you to go on and issue another I/O operation while the first one is
seeking).
If you turn on the bus master DMA option of IDE you can come close to
the speed of SCSI, but you still don't have the disconnect
capability. It still speeds up things somewhat when you're doing MD.
Note, however, that 2 year old drives generally don't have bus master
DMA capability.
I'm still surprised you didn't get any real-life speedup using the MD
driver, though. If you were partitioned decently you should have gotten
some benefit just from reduced head movement. If you had a swap partition
on one of those drives that makes a big difference, of course -- that's why
I went to 64mb of RAM (rarely touch swap). And if you were already partitioned
sensibly that should also have helped. Still... over on the Beowolf site
they did tests and found that with bus master DMA IDE they got 1.5 times
the performance by using the MD driver... so...
Oh. If you want the ultimate in performance, get the DPT hardware RAID
controller :-). (But what mere mortal can afford one for personal use?).
--
Eric Lee Green e_l_...@hotmail.com
Linux & Educational Administration computer solutions
cjk
wrong, the seagate hawk is a 5400 rpm drive.
by the way, the new 10,000 rpm scsi disk from IBM is faster than a
seagate cheetah. probably more reliable too.
christian klein
cklein1<at>ua1vm.ua.edu
Chris Mauritz
You might want to check Seagate's website before you continue spreading
incorrect information. The hawk drives are 7200rpm. Anyone who doubts
can check www.seagate.com for the specs from the horse's mouth.
> by the way, the new 10,000 rpm scsi disk from IBM is faster than a
> seagate cheetah. probably more reliable too.
Based on IBM's recent performance in making consumer grade hard
disks, I wouldn't hold your breath....
Ray Knight
James Turner wrote:
> Recently I have been considering doing an upgrade on my system,
> focusing on improving disk speed (both throughput and latency). Right
> now, I've got a fairly standard IDE setup (two hard drives, one two
> years old, one three years old) on separate cables (and channels).
> They are fine and work well, except for performance, which is why I am
> considering an upgrade in the next few months.
>
> Right now, I am looking at a Seagate Cheetah drive. Capacity is not
> really as important as speed, so the 4.5gig looks to be what I will
> get. Am I right in assuming this is the fastest SCSI drive for use
> under Linux?
>
> I have been reading old posts in Dejanews, and checking websites, and
> it appears that the SCSI controller of choice would be a Bus Logic
> BT-938 (forgive me if that's not the right model number, my notes are
> elsewhere). I am looking for stability and speed. Initially I had
> planned on an Adaptec 2940UW, but it would seem that the drivers in
> Linux are not as stable nor as efficient as the Bus Logic (or the
> Diamond Fireport, which I have also read good things about).
>
> Roughly, my needs are as follows. I'm getting very much into Linux
> development, and disk speed is definitely something I would like to
> improve. Right now I'm running an AMD K6-200 with 128meg RAM, and a
> fairly slow disk subsystem. I own a SCSI Zip drive (running through a
> 16bit ISA Future Domain controller). I would like to run both the
> Cheetah and the Zip from the same card, as well as in the future
> perhaps add a CD writer and/or a scanner.
>
> Any thoughts on the best SCSI card (as well as a different disk if my
> research in that area has gone wrong) would be greatly appreciated.
> Also, would purchasing a kit or an OEM card be best? Am I right in
> assuming that the OEM comes with no cables? Would it be cheaper just
> to buy the cables I need?
>
> Thanks in advance.
>
> --
> James Turner turn...@xtn.net
> http://cswww.vuse.vanderbilt.edu/~turnerj1/
The Symbios Logic 53C875 based cards (the Diamond Fireport is one)
provide excellent performance and drivers are available for almost any
OS. If you are looking for performance two 7200 rpm Ultra Wide drives
with the proper
setup of your file systems will give slightly better performance than a
single drive of twice the capacity. For example I run two 2.1 GB
Quantum Atlas II drives rather than the 4.2 GB Atlas II. The 2.1 GB
drives are not in as much demand as of late so prices are less than half
that of a single 4.2 GB drive. I purchase the Atlas drives from
www.basoncomputers.com for $239 each which is a very good price for 7200
rpm Ultra Wide SCSI drives.
John Binder
Ray Knight wrote:
Hi If the problem is the obj link time during code development I have had
good results with making a ram disk '/ram'of size ~30Megs and storing all
object code there (also put copies of the gcc libraries in /ram)
(I too have poor performing ide drives but the ram disk works exceedingly
well)
-John
Ville-Matti Kiili
Eric Lee Green <e_l_...@hotmail.com> wrote:
: If you turn on the bus master DMA option of IDE you can come close to
: the speed of SCSI, but you still don't have the disconnect
: capability. It still speeds up things somewhat when you're doing MD.
: Note, however, that 2 year old drives generally don't have bus master
: DMA capability.
I disagree. I used to have a Conner CFS420A hard disk (from '94, so it was
four years old) and I still have a Seagate ST31220A (from '95, three years
old), and they both support busmastering DMA without any problems. I don't
think these drives are just exceptions.