On Mon, 27 Oct 2003, Hermann Himmelbauer wrote:

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

It's possibly the "old Dual P-II-266" that may be slowing things down
here.

On one of my systems: (Dual Athlon 2.4 with 2 Promise PCI IDE cards and 4
drives):

From /proc/mdstat

md4 : active raid5 hdk6[3] hdi6[1] hdg6[2] hde6[0]
      176055936 blocks level 5, 32k chunk, algorithm 0 [4/4] [UUUU]

Single drive:

/dev/hdg6:
 Timing buffer-cache reads:   128 MB in  0.48 seconds =266.67 MB/sec
 Timing buffered disk reads:  64 MB in  1.49 seconds = 42.95 MB/sec

The array:

/dev/md4:
 Timing buffer-cache reads:   128 MB in  0.50 seconds =256.00 MB/sec
 Timing buffered disk reads:  64 MB in  0.97 seconds = 65.98 MB/sec

On another server (Dual PIII/Xeon 700MHz with SCSI drives)

md4 : active raid5 sdd6[3] sdc6[1] sdb6[2] sda6[0]
      23663424 blocks level 5, 32k chunk, algorithm 0 [4/4] [UUUU]

Single drive:

/dev/sdc6:
 Timing buffer-cache reads:   128 MB in  0.59 seconds =216.95 MB/sec
 Timing buffered disk reads:  64 MB in  3.39 seconds = 18.88 MB/sec

The array:

/dev/md4:
 Timing buffer-cache reads:   128 MB in  0.57 seconds =224.56 MB/sec
 Timing buffered disk reads:  64 MB in  0.75 seconds = 85.33 MB/sec

The array in this case is 4 disks, connected 2 disks to an on-board dual
Adaptec controller (It's a Dell 6xxx box)

It also has 2 PCI adaptec 7xxx cards connected to an external box with 8
drives:

md6 : active raid5 sdl2[7] sdh2[6] sdk2[5] sdg2[4] sdj2[3] sdf2[2] sdi2[1] sde2[0]
      62918016 blocks level 5, 32k chunk, algorithm 0 [8/8] [UUUUUUUU]

Single drive:

/dev/sdk2:
 Timing buffer-cache reads:   128 MB in  0.58 seconds =220.69 MB/sec
 Timing buffered disk reads:  64 MB in  4.00 seconds = 16.00 MB/sec

The array:

/dev/md6:
 Timing buffer-cache reads:   128 MB in  0.57 seconds =224.56 MB/sec
 Timing buffered disk reads:  64 MB in  1.03 seconds = 62.14 MB/sec

fast RAID array!

So my advice is that if you want speed, be prepared to spend the £££ to
get that speed (and I don't consider these servers particularly fast, but
they are fast enough for my application which is NFS & Samba serving a
small company of engineers (software/hardware) via a single 100MB/sec
Ethernet interface).

Gordon
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