LVM vs Veritas for Stripe & mirror ?

[Michael_238]

I have a rp7410 with mirrored root disks. THat is setup and running fine. I also have a 5300 storage device. I have 3 disks at 0,1,2 and 3 at 8,9,10 . I want to stripe 3 disks across a single lvol and then mirror that stripe set to the second set of disks. This 0+1 setup will house a sigle directory tree for a database and database application. After looking through the posts on this subject, I see some people attempting to do this through LVM and Mirrordisk/UX. But others suggest using the Veritas product which requires some purchase before you can mirror. My question to the forum is this: Would you suggest that I purchase the license for the Veritas VM or just make it happen with LVM? I appreciate any advice on this issue.

Michael Keefe

[James R. Ferguson · Accepted solution]

Hi Michael:

With LVM, as you know, you cannot utilize true stripes with mirroring, although you can use extent-based mirrored stripes. The essential difference is one of granularity. True stripes range in size from 4 to 32768 *kilo*bytes where extents range from 1-256 *mega*bytes.

Since you already license MirrorDisk/UX, I would give strong consideration to leveraging it again for your database.

Regards!

...JRF...

[James Murtagh]

Hi Michael,

I would suggest that you stick with LVM unless you have a requirement for any of the advanced features of VxVM, i.e. more that 3 mirror copies of the data, active/active multi-pathing. Check out the release notes for a full list of features:

http://www.docs.hp.com/hpux/onlinedocs/5187-1373/5187-1373.html

Apart from the cost of the additional license, there may be training costs as it is quite a complex product and you will need to be up to speed before introducing it to your environment. This may be multiplied if there are SAs other than yourself.

So if you don't need any of the advanced features and LVM can handle what you need to do then I would go with that. I don't believe there will be too much performance difference between them for the amount of disks you have.

Regards,

James.

[Jakes Louw_1]

You have 2 options:

micro-striping using the lvcreate -i -I etc.
or

makro-striping ...
create a PVG :
vgcreate -g PVG1 /dev/vg_new disk1 disk2 disk3....

then do the lvcreate so:
lvcreate -D y -s g -L size -n name etc.

The first option lets you stripe with minute granularity, but BEWARE: there are issues with LVEXTEND afterwards!!!
The second option is like a Humvee compared to a Civic, and yes it is extent-based, but works well, is extendable, and can be applied selectively if you wish, ie: lvextend can be done UNSTRIPED later by simply calling the right options in LVCHANGE!!!

Have fun!