Running slower after raid0

[Bruno Diniz]

Hi all,

I have a system with two S-ATA hard disks and I configured raid0 with them using mdadm. Each HD has 200GB of capacity. What is weird is that after configuring the raid, the newly created device (/dev/md0) is slower than each of the disks individually. Look at the numbers:

hdparm -Tt /dev/sda

/dev/sda:
 Timing cached reads:   3528 MB in  2.00 seconds = 1763.39 MB/sec
 Timing buffered disk reads:  170 MB in  3.01 seconds =  56.41 MB/sec


hdparm -Tt /dev/sdb

/dev/sdb:
 Timing cached reads:   3412 MB in  2.00 seconds = 1705.41 MB/sec
 Timing buffered disk reads:  180 MB in  3.01 seconds =  59.81 MB/sec


hdparm -Tt /dev/md0

/dev/md0:
 Timing cached reads:   3400 MB in  2.00 seconds = 1699.41 MB/sec
 Timing buffered disk reads:  134 MB in  3.04 seconds =  44.09 MB/sec

cat /etc/mdadm/mdadm.conf

DEVICE partitions
ARRAY /dev/md1 level=raid0 num-devices=2 UUID=b659b438:39b787dc:02f341ed:480bddf3
   devices=/dev/sdc3,/dev/sdd2
ARRAY /dev/md0 level=raid0 num-devices=2 UUID=4d999bad:c9c3cf0e:91fd35b1:57f5529c
   devices=/dev/sda1,/dev/sdb1

The /dev/md1 array is working correctly, and its bandwidth is twice as much as each individual disk bw. The only difference between md0 and md1 is their capacity and that md0 is formatted with XFS, while md1 uses Reiserfs.

What could be the problem? Could it be XFS?

Thanks,

Bruno.
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Bruno Diniz de Paula