[linux-lvm] lvm lowers transfer rate

[linux-lvm] lvm lowers transfer rate

[Innocent Azinyue Ndangoh]

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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Re: [linux-lvm] lvm lowers transfer rate

[William Blunn]

> 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?!?

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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Re: [linux-lvm] lvm lowers transfer rate

[Patrick Caulfield]

On Wed, Jul 24, 2002 at 09:16:36PM -0400, Innocent Azinyue Ndangoh wrote:
> 
> 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?!?

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