brien dieterle wrote:
>
>> I need your opinion on Linux software RAID. I mean its performace (in
>> terms of drive read/write time). I've configured Software RAID on two
>> SATA drives. I figured out the onboard SATA raid controller that this
>> server has is a fakeraid controller (Works only with the manufacturer
>> drivers on M$ Windoze). So, resorted to Linux software RAID. I've had
>> bad experience in the past with software RAID with 2.4 kernel based
>> Linux server. So, I'd like to know if anyone here has experiences with
>> software RAID on 2.6 kernel (default FC3 kernel).
>>
>> And by accident, I created three RAID devices (namely md0, md1 and md2
>> for /boot, / and swap respectively). Do I need to create RAID for swap
>> parition. Now, I'm worried that it's going to affect the performance. As
>> I write, it's still going thru FC3 installation process. Probably, I'd
>> perform some harddrive read/write access tests after installation. I'd
>> really appreciate if you can share your opinions and experiences with
>> software RAID in Linux 2.6 kernel (to be specific 2.6.9-smp).
>>
>> Thanks,
>> Sanjay.
>>
>
> I've been running software raid5 on / (with 3 ide drives, not SATA), for
> many months now with no problems whatsoever. In fact, I moved the array
> to a new machine and rearranged the drives onto different controllers
> without a hiccup.
>
> Swap on raid is probably recommended (if the swap device croaks while
> the system is using it bad things can happen). But, you are more than
> welcome to add the partitions in fstab and the kernel will stripe to all
> of them automatically, so no, raid is not required.
>
> Your raid1 (you didn't make raid0, did you?) device will probably be
> slightly slower than a single disk for reads, while a bit slower still
> for writes. I've done some benchmarking of several software and one
> hardware raid systems, with less than amazing results.
I set up a RH9 server with software raid1 on ide a little over a year
ago, and haven't had a problem (knock wood). The partition/definition
during installation was a tad tricky, but straight forward. In order to
provide fault tolerance, I decided to mirror the swap too.
I haven't done any performance measurements, but speeds aren't very
noticably different than what I'd expect to see on a single drive. In
theory, writes will be slower, and reads should be *faster*. I think
it's curious that Brien said that raid1 reads would be slightly slower.
I suppose that could be, but is not what I would expect. Meaningful
comparisons haven't been possible for me to do, due to lack of
equivalent hardware and time. ;)
>
> Please forgive the HTML below-- here is a table of some benchmarked
> systems. The fastest machine was Hardware Raid, but it also had 4 disks
> and much beefier hardware than most of the others. It's hard to tell--
> I'm mostly interested in block read/write, so I ommited other results to
> save space here.
>
>
>
> Sequential Output (writing to disk) Sequential Input (reading from disk)
>
>
>
>
>
>
>
>
>
>
>
> Per Chr block rewrite Per Chr Block
> host Kernel RaidType raidlevel #disks DiskType DiskSpeed (RPM)
> CPUInfo mhz RAM(M) testsize K/sec K/sec K/sec K/sec K/sec
> nat1-single disk 2.6.8 none
> 1 ide 5400 (1) Pentium 165mhz 165 128 6G 1491 10495 5256
> 1730 11514
> Xena raid1 2.4.22 Hardware 1 2 scsi 10000 (2) Intel(R) Pentium(R)
> III 1400Mhz 1400 2000 3G 15682 33073 12604 16394 24242
> Fred-degraded 2.6.7 Software 1 1 scsi 10000 (2) Pentium III
> (Coppermine) 1.0Ghz 1000 2000 10G 14862 20169 11823 16140 28471
> Fred raid1 2.6.7 Software 1 2 scsi 10000 (2) Pentium III
> (Coppermine) 1.0Ghz 1000 2000 10G 14653 19625 11453 16608 28788
> Fred single disk 2.6.7 Software 1 1 scsi 10000 (2) Pentium III
> (Coppermine) 1.0Ghz 1000 2000 10G 14808 22059 12871 16381 31871
> Bud raid1 2.4.22 Software 1 2 scsi 10000 (2) Intel(R) Xeon(TM)
> CPU 3.06Ghz 3000 1000 10G 24288 38629 21496 25724 48377
> squirrel single disk 2.6.9 none
> 1 ide 7200 (1) Intel(R) Pentium(R) 4 CPU 3.00Ghz 3000 512 10G
> 33913 35521 18886 26427 52242
> brien-degraded 2.6.9 Software 5 2 ide 7200 (2) Athlon XP
> 1.53Ghz 1500 512 10G 18619 20690 16483 26114 52297
> brien-raid5 2.6.9 Software 5 3 ide 7200 (2) Athlon XP 1.53Ghz
> 1500 512 10G 20756 20477 16935 26764 62454
> brien single disk 2.6.9 none
> 1 ide 7200 (2) Athlon XP 1.53Ghz 1500 512 10G 25492 33957
> 22044 27278 63052
> Gasp raid5 2.4.22 Hardware 5 4 scsi 10000 (2) Intel(R) Xeon(TM)
> CPU 2.80Ghz 2800 4000 10G 20936 24329 17461 25829 89098
>
>
> --brien
>
>
--
-Eric 'shubes'
"There is no such thing as the People;
it is a collectivist myth.
There are only individual citizens
with individual wills
and individual purposes."
-William E. Simon (1927-2000),
Secretary of the Treasury (1974-1977)
"A Time For Truth" (1978), pg. 237
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