RE: md on partition

I guess Neil was wrong, or I misunderstood something.
Were both test with the same RAID and LVM config?  Or was 1 RAID0 and the
other RAID5?

If RAID5, are you sure the resync was done before you did your tests?
"cat /proc/mdstat" to determine this.

Yes, size does matter!  Chunk size that is.  Not sure about extent size.

As long as the only difference was the whole disk vs partitions, then
partitions make a big difference!  This sucks!

Guy

-----Original Message-----
From: linux-raid-owner@xxxxxxxxxxxxxxx
[mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Ming Zhang
Sent: Saturday, October 23, 2004 11:52 AM
To: Guy
Cc: linux-raid@xxxxxxxxxxxxxxx
Subject: RE: md on partition

thx but i met this problem.

i use 4 x 400GB SATA disks, i make a raid 0 or 5, and build a vg on top
of md, then use bonnie++ to test read performance.

LVM (MD = sda+sdb+..) = 95MBsec, md is built on top of whole disk.

LVM (MD = sda1+sdb1+.) = 48MBsec, md is built on top of each partition.

so where is the problem? does md chunk size matter? or lvm extent size
matters? thx.


ming

On Sat, 2004-10-23 at 02:07, Guy wrote:
> I found this old message:
> "On Tuesday June 1, maheshext3@xxxxxxxxx wrote:
> > 
> > --- Neil Brown <neilb@xxxxxxxxxxxxxxx> wrote:
> > > 
> > > What does
> > >    ls -l /dev/hd[eg]5
> > > show? How about
> > >    cat /proc/partitions
> > >    dd if=/dev/hde5 of=/dev/null bs=1024k
> > 
> > Thanks a lot, Neil, turns out those nodes were not present. After I 
> > mknod'd them, all's fine in RAIDland...
> >   Quick question: does using extended partitions for RAID affect 
> > performance?
> 
> The fact that the partitions are "extended" is invisible to most of the
> kernel, and it could not have any affect of performance.
> 
> NeilBrown"
> 
> Guy
> 
> -----Original Message-----
> From: linux-raid-owner@xxxxxxxxxxxxxxx
> [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Ming Zhang
> Sent: Friday, October 22, 2004 1:28 PM
> To: linux-raid@xxxxxxxxxxxxxxx
> Subject: md on partition
> 
> Hi folks.
> 
> I remembered that there was a discussion on the list about some abnormal
> performance penalty if u use a partition instead of a whole disk for MD.
> But I could not find this discussion via archival or google.
> 
> Could somebody be kindly enough to point me to the right spot? Thanks a
> lot.
> 
> Ming
> 
> 
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-- 
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| Ming Zhang, PhD. Student
| Dept. of Electrical & Computer Engineering
| College of Engineering
| University of Rhode Island
| Kingston RI. 02881
| e-mail: mingz at ele.uri.edu
| Tel. (401) 874-2293 
| Fax. (401) 782-6422
| http://www.ele.uri.edu/~mingz/
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