Moving a raid5 array

Moving a raid5 array

[Clive Messer]

I currently have a 4 disk raid5 array which I wish to move to another machine. 
In the current machine it is comprised of sda1/sdb1/sdc1/sdd1. When I move it 
to the new machine the disks will all shift up by 2. ie. the partitions will 
now be sdc1/sdd1/sde1/sdf1. If I 'mdadm --assemble' the array on the new 
machine with the new partition names will md figure it all out or am I going 
to trash my data?

For reference my current mdadm.conf ......

DEVICE /dev/sd*[0-9]
ARRAY /dev/md0 level=raid5 num-devices=4 
UUID=f1949e2c:bec621e4:de55ae15:4f336899

Regards

Clive
-- 
Clive Messer <clive@vacuumtube.org.uk>

Re: Moving a raid5 array

[Neil Brown]

On Tuesday September 12, clive@vacuumtube.org.uk wrote:
> 
> I currently have a 4 disk raid5 array which I wish to move to another machine. 
> In the current machine it is comprised of sda1/sdb1/sdc1/sdd1. When I move it 
> to the new machine the disks will all shift up by 2. ie. the partitions will 
> now be sdc1/sdd1/sde1/sdf1. If I 'mdadm --assemble' the array on the new 
> machine with the new partition names will md figure it all out or am I going 
> to trash my data?
> 
> For reference my current mdadm.conf ......
> 
> DEVICE /dev/sd*[0-9]
> ARRAY /dev/md0 level=raid5 num-devices=4 
> UUID=f1949e2c:bec621e4:de55ae15:4f336899

Providing you don't already have a /dev/md0 on the new machine, which
should work perfectly - no confusion.

NeilBrown

Re: Moving a raid5 array

[Clive Messer]

On Tuesday 12 September 2006 17:21, Neil Brown wrote:
> On Tuesday September 12, clive@vacuumtube.org.uk wrote:
> > I currently have a 4 disk raid5 array which I wish to move to another
> > machine. In the current machine it is comprised of sda1/sdb1/sdc1/sdd1.
> > When I move it to the new machine the disks will all shift up by 2. ie.
> > the partitions will now be sdc1/sdd1/sde1/sdf1. If I 'mdadm --assemble'
> > the array on the new machine with the new partition names will md figure
> > it all out or am I going to trash my data?
> >
> > For reference my current mdadm.conf ......
> >
> > DEVICE /dev/sd*[0-9]
> > ARRAY /dev/md0 level=raid5 num-devices=4
> > UUID=f1949e2c:bec621e4:de55ae15:4f336899
>
> Providing you don't already have a /dev/md0 on the new machine, which
> should work perfectly - no confusion.

Thanks Neil. Appreciate the quick response.

Regards

Clive
-- 
Clive Messer <clive@vacuumtube.org.uk>

I think there is a trick to improve performance of md.

[liyiming]

blow are some codes in md_do_sync function of md.c in 
linux-2.6.17.11-rc5/drivers/md

4774: int next = (last_mark+1) % SYNC_MARKS;

I have no idea why SYNC_MARKS is set 10. if set SYNC_MARKS to 8 or 
16(the power of 2), we can replace the % operation to  & operation
and this trick will accelerate the running of this code.