RE: md on partition

On Sat, 2004-10-23 at 18:52, Guy wrote:
> You said:
> "will raid by default choose different chunk size if device size is
> different, for example, sda is 400GB while sda1 is 50GB?"
> 
> No, but the random seek test will give different results.  50GB will perform
> better, since less head travel.
> 
> Why the difference?  I would want everything the same for both tests.
> 
so assume raid use same chunk size for both 50GB partition and 400GB
disk, i can not understand why here a near half performance down grade.

> Guy
> 
> -----Original Message-----
> From: linux-raid-owner@xxxxxxxxxxxxxxx
> [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Ming Zhang
> Sent: Saturday, October 23, 2004 6:39 PM
> To: Guy
> Cc: linux-raid@xxxxxxxxxxxxxxx
> Subject: RE: md on partition
> 
> 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@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
> > > 
> > > 
> > > -
> > > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
-- 
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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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