My P4-2.4GHz with 3 WD80G 8MB caches does significantly better with RAID5

hdparm -tT /dev/md/3

/dev/md/3:
 Timing buffer-cache reads:   1844 MB in  2.00 seconds = 921.08 MB/sec
 Timing buffered disk reads:  166 MB in  3.00 seconds =  55.26 MB/sec

md3 : active raid5 ide/host4/bus0/target0/lun0/part3[1]
                            ide/host2/bus1/target0/lun0/part3[2]
                            ide/host2/bus0/target0/lun0/part3[0]
      143713280 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

Linux why 2.4.22-ck2-blackbox-aph-21 #1 Wed Sep 17 09:41:14 EDT 2003 i686
GNU/Linux

This kernel also has the low latency and preempt patches applied and running
at 500hz.

Andrew


----- Original Message ----- 
From: "Hermann Himmelbauer" <redacted>
To: "Gordon Henderson" <redacted>; <redacted>
Sent: Monday, October 27, 2003 6:01 AM
Subject: Re: RAID1 VS RAID5

On Monday 27 October 2003 10:19, Gordon Henderson wrote:

quoted

On Mon, 27 Oct 2003, Hermann Himmelbauer wrote:

quoted

My experience is that software RAID5 is quite slow.

My experiences are the opposite to yours I'm afraid - I've not found it
any slower than a single drive and in some cases a lot faster!

A lot depends on exactly what you are doing with it though, but I'm
willing to sacrifice some speed for data integrity.

Most of my systems are network servers with 100Mb Network cards fitted -
as long as my disk systems are faster than 12.5MB/sec I'm happy. In
practice I can stream 50MB/sec+ out of some simple RAID5 IDE systems I
have.

Well - I have an old Dual P-II-266 System with an onboard SCSI-Controller

with

3 Ultra SCSI-disks connected, building a RAID5. I did a simple Test with
"hdparm -tT" to provide you with numbers:

/dev/sdb:
 Timing buffer-cache reads:   128 MB in  1.46 seconds = 87.67 MB/sec
 Timing buffered disk reads:  64 MB in  5.07 seconds = 12.62 MB/sec

/dev/sdc:
 Timing buffer-cache reads:   128 MB in  1.47 seconds = 87.07 MB/sec
 Timing buffered disk reads:  64 MB in  4.78 seconds = 13.39 MB/sec

/dev/sdd:
 Timing buffer-cache reads:   128 MB in  1.49 seconds = 85.91 MB/sec
 Timing buffered disk reads:  64 MB in  5.05 seconds = 12.67 MB/sec

So you see, the seperate disks achieve ~ 13MB/s. My RAID5 raidtab looks

like

this:
raiddev /dev/md0
        raid-level              5
        nr-raid-disks           3
        nr-spare-disks          0
        chunk-size              4
        persistent-superblock   1
        parity-algorithm        left-symmetric
        device                  /dev/sdb2
        raid-disk               0
        device                  /dev/sdc2
        raid-disk               1
        device                  /dev/sdd2
        raid-disk               2

And "hdparm -tT" looks like this:

/dev/md0:
 Timing buffer-cache reads:   128 MB in  1.45 seconds = 88.28 MB/sec
 Timing buffered disk reads:  64 MB in 13.85 seconds =  4.62 MB/sec

So this is ~ 1/3rd of the read performance of a single disk. And this is

what

a appr. measure when copying files etc.

My kernel version is 2.4.20 and the CPU-Load during the hdparm test is

only at

~ 30%.

Best Regards,
Hermann

-- 
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