topic Re: Mirroring question in Operating System - HP-UX

Mirroring question

Lacrosse — Mon, 31 Mar 2003 14:07:36 GMT

I received an error when attempting to mirror the database volume.
ERROR:
The command used to extend logical volumes, /sbin/lvextend, has failed. The stderr output from the command is shown below. The logical volume has not been extended.

lvextend: Couldn't extend the logical volume:
A physical extent described by the extent array is already in use, or a sparing operation is in progress.
lvextend: The LVM device driver could not extend the
logical volume "/dev/vg01/lvol5".

This volume is striped across 2 disk can you mirror a striped volume????

Re: Mirroring question

Jeff Schussele — Mon, 31 Mar 2003 14:14:01 GMT

Hi,

Nope - you can't mirror a standard striped LV.

You can mirror if you use extent-based striping (lvcreate -D y) in a PVG (Physical Volume group). But then you're limited to the stripe size being equal to the extent size.

Rgds,
Jeff

Re: Mirroring question

Michael Duthie — Mon, 31 Mar 2003 14:17:03 GMT

The built in striping (-i -I) with LVM does not work with mirroring. You should use extent striping with the -D option during lvcreate.

Re: Mirroring question

A. Clay Stephenson — Mon, 31 Mar 2003 14:19:40 GMT

The answer is no (almost). You can mirror using extent based striping but then the striping is done in PE-sized chunks so that the performance benefits from striping are almost nil because the chunks are so large. (e.g. 4MB vs 64k).

You can look into the Veritas volume manager (VxVM) that will give you more flexibility but frankly, I have not been too impressed with it and it does impose a noticable overhead (~ 5%) on the system.

Re: Mirroring question

David Burgess — Mon, 31 Mar 2003 14:25:32 GMT

It all looks a bit messy. Take a look at these they may help :-

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x9cbc4e49c5cdd5118ff40090279cd0f9,00.html

This is for hpux 9, but gives you an idea of the scripting process that is invoved :-

http://aa11.cjb.net/hpux_admin/1997/0301.html

Regards,

Dave

Re: Mirroring question

Michael Duthie — Mon, 31 Mar 2003 14:26:31 GMT

Usually when extent striping is used the PE size is taken done to 1MB but there is a limitation to the number of PEs you can have on one spindle and with the bigger disks we have these days it could leave lots of unable disk. The max PE is 65535.

Re: Mirroring question

Donald Kok — Mon, 31 Mar 2003 15:02:38 GMT

For striping with mirrorring (RAID 0/1) you need at least 4 disks.
Greetzz
Donald