Disk copy

[Tim Stallman]

Hi,
What is the best way to do a disk copy? I am wanting to clone a disk and I'm looking for the quickest way to do this (and I do not want to use ignite).

Thx,
Tim

[Robert-Jan Goossens]

Hi Tim,

Not quite sure what you would like to do but,

dd if=/dev/rdsk/c?t?d? of=/dev/rdsk/c?t?d? bs=1024k

will copy the disk.

Hope it helps,

Robert-Jan.

[John Palmer]

If the disks are identical, dd will do the trick...

dd if=/dev/rdsk/??? of=/dev/rdsk/??? bs=64k

Make sure you have the correct output disk though ;-)

Regards,
John

[melvyn burnard]

dd does work, but be aware it is a bit-by-bit copy, and if the source has errors, it will copy those across as well.

[MANOJ SRIVASTAVA]

dd is device to device copy , you can copy disk to disk using it , however if u ahve mirror ux then u can also use lvm to do the job ,

in case you have EMC then there are ltos of time finder option to do the same.



Manoj Srivastava

[Tim Stallman]

does it matter what bs I use or can I take the default. My file systems are hfs with the default block size.

Thx,
Tim

[Tom Jackson]

Hi Tim:

I have a cron job that copies disks every night here's the code:

#!/bin/ksh
echo "starting mirror_cathm208 at `date`" > /tmp/mirror_208data 2>&1
echo "dd the disks..." >> /tmp/mirror_208data 2>&1
/usr/bin/dd if=/dev/vg01/rlvol1 of=/dev/vg03/rlvol1 bs=64k >> /tmp/mirror_208dat
a 2>&1
/usr/bin/dd if=/dev/vg01/rlvol2 of=/dev/vg03/rlvol2 bs=64k >> /tmp/mirror_208dat
a 2>&1
/usr/bin/dd if=/dev/vg01/rlvol3 of=/dev/vg03/rlvol3 bs=64k >> /tmp/mirror_208dat
a 2>&1

echo "fsck the disks..." >> /tmp/mirror_208data 2>&1
/usr/sbin/fsck -F vxfs -y /dev/vg03/rlvol1 >> /tmp/mirror_208data 2>&1
/usr/sbin/fsck -F vxfs -y /dev/vg03/rlvol2 >> /tmp/mirror_208data 2>&1
/usr/sbin/fsck -F vxfs -y /dev/vg03/rlvol3 >> /tmp/mirror_208data 2>&1

echo "done at `date`" >> /tmp/mirror_208data 2>&1

The above code is for data disks. I have another script for my system disk. The system disk requires some additional steps. Let me know if you're interested.

Tom

[John Palmer]

The block size you tell dd is the buffer size it will use for I/O, nothing to do with the filesystem blocksize.

If you default it, dd uses 512 bytes which is slooooooow. From experiment, anything above 8k appears to give optimal performance.

Regards,
John

[Robert-Jan Goossens · Accepted solution]

Hi Tim,

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x464d5c7609e9d61190050090279cd0f9,00.html

discussion about blocksize.

Kind regards.

Robert-Jan.

[James R. Ferguson]

Hi Tim:

To add to John's suggestions, just make sure to use the character disk device (/dev/rdsk). You don't want to impose needless overhead through LVM.

Regards!

...JRF...

[Oleg Zieaev_1]

Tim,

applying dd to rdsk is also much faster.
This is also true for rlvols.

Hope this helps.
0leg