20040526: raid configuration file parameters (cont.)

>From: Tom Yoksas <address@hidden>
>Organization: UCAR/Unidata
>Keywords:  200405270011.i4R0BjtK010667 LDM Linux RAID JFS

Hi Gerry,

So, I looked at the /etc/raidtab and /etc/raidtab.old files on
bigbird and compared them to the /etc/raidtab file on our dual
Athlon MP 2800+ machine:

/etc/raidtab from bigbird:

[ldm@bigbird ~]$ cat /etc/raidtab

#
# 'persistent' RAID5 setup, with no spare disks:
#  modified (cleaned up) 2004 05 26, GCreager

raiddev /dev/md0
    raid-level                5
    nr-raid-disks             7
    nr-spare-disks            1
    persistent-superblock     1
    chunk-size                4

    device                    /dev/hde1
    raid-disk                 0

    device                    /dev/hdg1
    raid-disk                 1

    device                    /dev/hdi1
    raid-disk                 2

    device                    /dev/hdk1
    raid-disk                 3

    device                    /dev/hdm1
    raid-disk                 4

    device                    /dev/hdo1
    raid-disk                 5

    device                    /dev/hdq1
    raid-disk                 6

    device                    /dev/hds1
    spare-disk                0
#    raid-disk                 7

#    device                    /dev/hdl2
#    spare-disk                0

#    device                    /dev/hdt1
#    spare-disk                1


/etc/raidtab from UPC dual Athlon MP 2800+ machine, created by Linux
OS install

[ldm@dhcp14 ~]$ cat /etc/raidtab
raiddev             /dev/md0
raid-level                  0
nr-raid-disks               2
chunk-size                  64
persistent-superblock       1
nr-spare-disks              0
    device          /dev/hde1
    raid-disk     0
    device          /dev/hdg1
    raid-disk     1

Two things:

1) your new raidtab file seems to have conflicting info in it:

 ...
    nr-spare-disks            1
 ...
    spare-disk                0

2) the chunk-size specified in your raidtab file seems awfully small:

    chunk-size                4

   Compare this with the size for our RAID: 64.  Our size was chosen
   by the Linux installation itself.  I am wondering if the performace
   would be better if the chunk-size was larger (like 128K) and
   the file system formated with larger blocks?

   Don't you think that a chunk-size of 4K is awfully small?

Tom
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