lvm lowers transfer rate

Hi there,

I have 4 fiber channel disks, on which I intend to build a logical volume using lvm. Before creating the logical volume, I run an I/O test on the disks, which revealed that the disks each would do 10MBytes/sec I/Os.

However, when I create a logical volume, spanning all 4 disks using RAID0, I realize that the transfer rate now drops. Instead (10 * 4)MB/s, I get something close to 30MB/s. Am I doing something wrong?!?

My procedure to create logical volume:
1. Do fdisk on drive
- do -o (DOS option).
PS : setting the type to linux lvm(8e) results in errors on creating the logical volu7me
- do pvcreate on the disk(s)
- do vgcreate on all physical volumes requested
- do lvcreate on created volume
- mkfs.ext2 on logical volume
- mount log. volume

thanks for your time

Innocent

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10 MB/s ?

How are you measuring your data transfer rate?

Measured using "hdparm -t", a single Maxtor D740X IDE drive (80GB = GBP£72.00 or USD$113) will shift about 39 MB/s.

Bill

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I have found that striping Fibre-Channel only gives a performance boost up to 3 disks. I'm not sure whether that's a restriction of the FC interface I'm using (emulex) or the Linux driver but it's certainly consistent with what you're seeing.

patrick