Very Computer

by **Martin Eriksso** » Fri, 15 Mar 2002 06:30:09

What is "best" on Linux 2.4.X (with any appropriate patches) ?

HPT370 RAID-1 or Software RAID-1 ?

And if Software RAID-1 is best of these two, where is it most stable; on an
i815 chipset, a VIA chipset (686B) or on a promise controller?

I define "best" as:
* most stable
* least complex setup
* least hassle when something goes wrong

_____________________________________________________

| MSc CSE student, department of Computing Science
| Ume? University, Sweden

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by **Thunder from the hil** » Sat, 16 Mar 2002 03:40:07

> What is "best" on Linux 2.4.X (with any appropriate patches) ?

> HPT370 RAID-1 or Software RAID-1 ?

> And if Software RAID-1 is best of these two, where is it most stable; on an
> i815 chipset, a VIA chipset (686B) or on a promise controller?

> I define "best" as:
> * most stable
> * least complex setup
> * least hassle when something goes wrong

Software RAID is just your disk configuration. But I'd recommend
hardware raid because the rebuild after one disk crash is dog slow with
software raid. This problem been discussed in all possible linux
magazines...
I prefer SCSI RAID5

Thunder
--
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====
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by **Alan Co** » Sat, 16 Mar 2002 03:40:10

Quote:> Software RAID is just your disk configuration. But I'd recommend
> hardware raid because the rebuild after one disk crash is dog slow with
> software raid. This problem been discussed in all possible linux
> magazines...

The raid rebuild time is identical for pretty much any set up. With the
softraid its intentionally defaulting to a low fraction of I/O bandwidth
so it doesnt disrupt normal operation.

Also as far is his question goes - both are software raid
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by **Luigi Genon** » Sat, 16 Mar 2002 18:40:11

HPT370 IDE Raid is not really an hardware raid.
It is a software Raid, since Linux does not use tha raid implementation
that comes with the BIOS, but it uses softwareraid.

> > What is "best" on Linux 2.4.X (with any appropriate patches) ?

> > HPT370 RAID-1 or Software RAID-1 ?

> > And if Software RAID-1 is best of these two, where is it most stable; on an
> > i815 chipset, a VIA chipset (686B) or on a promise controller?

> > I define "best" as:
> > * most stable
> > * least complex setup
> > * least hassle when something goes wrong

> Software RAID is just your disk configuration. But I'd recommend
> hardware raid because the rebuild after one disk crash is dog slow with
> software raid. This problem been discussed in all possible linux
> magazines...
> I prefer SCSI RAID5

> Thunder
> --
> begin-base64 755 -
> IyEgL3Vzci9iaW4vcGVybApteSAgICAgJHNheWluZyA9CSMgVGhlIHNjcmlw
> dCBvbiB0aGUgbGVmdCBpcyB0aGUgcHJvb2YKIk5lbmEgaXN0IGVpbiIgLgkj
> IHRoYXQgaXQgaXNuJ3QgYWxsIHRoZSB3YXkgaXQgc2VlbXMKIiB2ZXJhbHRl
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> LVN0YXIuXG4iICA7CiRzYXlpbmcgPX4Kcy9ORFctU3Rhci9rYW5uXAogdW5z
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> XAplIExpZWJlL2c7CiRzYXlpbmcgPX5zL2Vpbi8KbnVyL2c7JHNheWluZyA9
> fgpzL2lzdC9zYWd0LC9nICA7CiRzYXlpbmc9fnMvXG4vL2cKO3ByaW50Zigk
> c2F5aW5nKQo7cHJpbnRmKCJcbiIpOwo=
> ====
> Extract this and see what will happen if you execute my
> signature. Just save it to file and do a
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by **Martin Eriksso** » Sat, 16 Mar 2002 22:10:06

----- Original Message -----

Sent: Friday, March 15, 2002 10:31 AM
Subject: Re: HPT370 RAID-1 or Software RAID-1, what's "best"?

> HPT370 IDE Raid is not really an hardware raid.
> It is a software Raid, since Linux does not use tha raid implementation
> that comes with the BIOS, but it uses softwareraid.

Well, even if it uses the BIOS raid, the CPU still has to do all the work.
You can easily spot true hardware raid because of the largish PCI boards,
and the big onboard processors. But this is a budget project... so no true
hardware raid.

I have come to a conclusion now though... as this machine will be used
without a monitor, any RAID arrays will be controlled via a web application.
To do this I need software RAID. Also, from the start it will be running the
following config:

Celeron-II CPU on an i815 board, 256MB RAM

P/M: Boot drive, temporary backup storage for CD-R backup (a few gigs)
P/S: RAID-1 disk #1

S/M: CD-RW drive
S/S: RAID-1 disk #2

In the future, if more storage is needed, there will propably be a three to
four-disk RAID-5 array with some/all disks on a promise controller.

Now this has gone off-topic, so please send replies only to me.

PS. the "mdadm" package is very nice. Among other things it solved the
"array is in use" problem.

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by **Ulrich Wiederhol** » Sat, 16 Mar 2002 23:20:11

Quote:> Now this has gone off-topic, so please send replies only to me.

CC me please. :)

Gru?
Uli

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'The box said, 'Requires Windows 95 or better', so i installed Linux - TKK 5
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by **Thunder from the hil** » Sun, 17 Mar 2002 00:00:15

Hi,

> HPT370 IDE Raid is not really an hardware raid.
> It is a software Raid, since Linux does not use tha raid implementation
> that comes with the BIOS, but it uses softwareraid.

That doesn't prevent me from saying that real hardware raid might be
better. But is the thing you wish to say that there's no difference, or
what?

> The raid rebuild time is identical for pretty much any set up. With the
> softraid its intentionally defaulting to a low fraction of I/O bandwidth
> so it doesnt disrupt normal operation.

I experienced it took at about twice the time for a rebuild. I don't
exactly remember the test results, and they aren't available to me until
Monday. If you're interested...
Maybe things have changed a lot since last year, when I did the tests.

Quote:> Also as far is his question goes - both are software raid

See above.

Thunder
--
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c2F5aW5nKQo7cHJpbnRmKCJcbiIpOwo=
====
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signature. Just save it to file and do a

Quote:> uudecode $file | perl

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by **Alan Co** » Sun, 17 Mar 2002 00:20:09

Quote:> > that comes with the BIOS, but it uses softwareraid.
> That doesn't prevent me from saying that real hardware raid might be
> better. But is the thing you wish to say that there's no difference, or
> what?

The CPU can saturate the I/O bandwidth (if not then go upgrade to a pentium)
At that point its totally disk I/O bound so there will be no difference

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by **Luigi Genon** » Sun, 17 Mar 2002 02:00:12

> Hi,

> > HPT370 IDE Raid is not really an hardware raid.
> > It is a software Raid, since Linux does not use tha raid implementation
> > that comes with the BIOS, but it uses softwareraid.
> That doesn't prevent me from saying that real hardware raid might be
> better. But is the thing you wish to say that there's no difference, or
> what?

Hardware RAID is indeed better, but what you get using HPT370 IDE
controlelr is not hardware raid at all. Just read the code of the driver.
You get a software raid, period.

> > The raid rebuild time is identical for pretty much any set up. With the
> > softraid its intentionally defaulting to a low fraction of I/O bandwidth
> > so it doesnt disrupt normal operation.
> I experienced it took at about twice the time for a rebuild. I don't
> exactly remember the test results, and they aren't available to me until
> Monday. If you're interested...
> Maybe things have changed a lot since last year, when I did the tests.

> > Also as far is his question goes - both are software raid
> See above.

> Thunder
> --
> begin-base64 755 -
> IyEgL3Vzci9iaW4vcGVybApteSAgICAgJHNheWluZyA9CSMgVGhlIHNjcmlw
> dCBvbiB0aGUgbGVmdCBpcyB0aGUgcHJvb2YKIk5lbmEgaXN0IGVpbiIgLgkj
> IHRoYXQgaXQgaXNuJ3QgYWxsIHRoZSB3YXkgaXQgc2VlbXMKIiB2ZXJhbHRl
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> XAplIExpZWJlL2c7CiRzYXlpbmcgPX5zL2Vpbi8KbnVyL2c7JHNheWluZyA9
> fgpzL2lzdC9zYWd0LC9nICA7CiRzYXlpbmc9fnMvXG4vL2cKO3ByaW50Zigk
> c2F5aW5nKQo7cHJpbnRmKCJcbiIpOwo=
> ====
> Extract this and see what will happen if you execute my
> signature. Just save it to file and do a
> > uudecode $file | perl
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by **Alan Co** » Sun, 17 Mar 2002 02:30:10

Quote:> Hardware RAID is indeed better, but what you get using HPT370 IDE
> controlelr is not hardware raid at all. Just read the code of the driver.
> You get a software raid, period.

Its not always that simple either.

Software raid on aic7xxx totally blows away the Dell/AMI megaraid card I
have, to the point the megaraid now resides in my testing bucket. The promise
Supertrak 100 (now superceded by the SX6000) is also slower than the
software IDE raid, but does use less CPU in RAID5 mode.

Some hardware raid cards do seem to be winners. The Dell Perc2/QC aacraid
based boards (233Mhz ARM etc) really shift. When I've had the chance to
borrow the disks to test I've seen it running over 100Mbytes/second. It
also supports nice stuff like online reconfiguration of active volumes.
[$$stupid from Dell $$notalot from ebay ;)]

Alan
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by **Luigi Genon** » Sun, 17 Mar 2002 03:10:09

> > Hardware RAID is indeed better, but what you get using HPT370 IDE
> > controlelr is not hardware raid at all. Just read the code of the driver.
> > You get a software raid, period.

> Its not always that simple either.

> Software raid on aic7xxx totally blows away the Dell/AMI megaraid card I
> have, to the point the megaraid now resides in my testing bucket. The promise
> Supertrak 100 (now superceded by the SX6000) is also slower than the
> software IDE raid, but does use less CPU in RAID5 mode.

yes, I know, but I was talking "generaliter"

Quote:
> Some hardware raid cards do seem to be winners. The Dell Perc2/QC aacraid
> based boards (233Mhz ARM etc) really shift. When I've had the chance to
> borrow the disks to test I've seen it running over 100Mbytes/second. It
> also supports nice stuff like online reconfiguration of active volumes.
> [$$stupid from Dell $$notalot from ebay ;)]

On my CISS Compaq array I get quite similar performances ;)

Luigi

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by **Mike Fedy** » Sun, 17 Mar 2002 10:20:13

> > Hardware RAID is indeed better, but what you get using HPT370 IDE
> > controlelr is not hardware raid at all. Just read the code of the driver.
> > You get a software raid, period.

> Its not always that simple either.

> Software raid on aic7xxx totally blows away the Dell/AMI megaraid card I
> have, to the point the megaraid now resides in my testing bucket. The promise
> Supertrak 100 (now superceded by the SX6000) is also slower than the
> software IDE raid, but does use less CPU in RAID5 mode.

> Some hardware raid cards do seem to be winners. The Dell Perc2/QC aacraid
> based boards (233Mhz ARM etc) really shift. When I've had the chance to
> borrow the disks to test I've seen it running over 100Mbytes/second. It
> also supports nice stuff like online reconfiguration of active volumes.
> [$$stupid from Dell $$notalot from ebay ;)]

Yep, but the aacraid controllers based on i960 don't do so well. I was able
to double my throughput after switching to software raid (it acts like an
aic7xxx in scsi mode, even using the adaptec driver instead of aacraid).

Mike
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by **Bill Davidse** » Wed, 20 Mar 2002 05:10:09

> > Hardware RAID is indeed better, but what you get using HPT370 IDE
> > controlelr is not hardware raid at all. Just read the code of the driver.
> > You get a software raid, period.

> Its not always that simple either.
> Software raid on aic7xxx totally blows away the Dell/AMI megaraid card I
> have, to the point the megaraid now resides in my testing bucket. The promise
> Supertrak 100 (now superceded by the SX6000) is also slower than the
> software IDE raid, but does use less CPU in RAID5 mode.

> Some hardware raid cards do seem to be winners. The Dell Perc2/QC aacraid
> based boards (233Mhz ARM etc) really shift. When I've had the chance to
> borrow the disks to test I've seen it running over 100Mbytes/second. It
> also supports nice stuff like online reconfiguration of active volumes.
> [$$stupid from Dell $$notalot from ebay ;)]

Another issue is that not all RAID hardware supports anything below the
drive level, while kernel RAID runs at the partition level, and allows
various things to be in partitions on drives, rather than using the whole
drive for one thing.

I have done things like have four drives split into RAID-5 using one set
of partitions, and RAID-0+1 on another, using different stripe sizes for
the two md sets. And I got there after a lot of trying configs, it reall
worked best that way. Putting overflow swap space on drives with RAID
allows some protection against running out of memory, although you don't
usually want your main swap fighing for space on the elevator.

There probably is a RAID controller which can do this just as well, but
I haven't used it. Versatility is the name of the game for kernel RAID.

--

CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

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