RE: md on partition

[Ming Zhang <mingz@ele.uri.edu>]

On Sat, 2004-10-23 at 12:12, Guy wrote:
> 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?
yes, if i tested RAID0, then will use RAID0 for both partition or whole
disk scenarios.

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

> Yes, size does matter!  Chunk size that is.  Not sure about extent size.
> 
will raid by default choose different chunk size if device size is
different, for example, sda is 400GB while sda1 is 50GB?

> 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@vger.kernel.org
> [mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Ming Zhang
> Sent: Saturday, October 23, 2004 11:52 AM
> To: Guy
> Cc: linux-raid@vger.kernel.org
> 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@yahoo.com wrote:
> > > 
> > > --- Neil Brown <neilb@cse.unsw.edu.au> 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@vger.kernel.org
> > [mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Ming Zhang
> > Sent: Friday, October 22, 2004 1:28 PM
> > To: linux-raid@vger.kernel.org
> > 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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| Dept. of Electrical & Computer Engineering
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| University of Rhode Island
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