Re: Software RAID on SATA drives]

> 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.

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