LVM, Mirror and Striping

[David Preston_4]

Hi, Over the weekend I installed some new disks, and I tried to set them up with Mirroring and Striping, but got an error message saying that I could either Mirror or stripe but not both. Is this true?
I am on 10.20. Does it change at 11.x?

DAve

[Trond Haugen]

First of all you should start thinking about upgrading to 11.x as 10.20 will be obsoleeted 6/30/03.
As for mirroring and striping I belive you could do that but will have to do it using the commandline. Further more you would need at least 4 disks; two for the striping and another two for the mirror. Remembet that there is no "original" but two copies. So if you stripe and mirror with two disks you realy only get a mirror.

Regards,
Trond

[Tom Geudens]

Hi Dave,
Sounds logical (not 100% sure, might be due to the options you use in the lvcreate). There seems to be no difference between 10.20 and 11.0 (the two versions I've got here).

However, take a look at the -D option (there 's an example of how to implement it in the manpages as well). Might be the best tradeoff ...

Regards,
Tom

[Stefan Farrelly · Accepted solution]

There are 2 ways to do it;

1. Use the -D (distributeed) option under lvcreate. This will allow striping+mirroring

2. use lextend manually. This will also allow you to stripe and mirror but your limited to the extent size (normally 4Mb) whereas in 1. above you can use smaller stripe values (usually around 64k is best).

[David Preston_4]

Thanks for the feedback.
1) yes I know I need to move to 11.x, that's the next project, but I needed the disk added.
2) I did have 6 disks I was adding to the group, intending on Mirroring and striping 3 disks per channel.
3) It looks like the -D was what I needed. so Inow I can plan for changing to this for my 11.i install.

Thanks again
Dave

[harry d brown jr]

You can do "extent based" striping and mirroring in 10.20.

live free or die
harry

[Tim D Fulford]

Dave

The above correct, you can mirror & stripe in LVM using extent based striping. However, the reason why you got errors is because you tried to use:

lvextend -m 1 -i -I ....

This is called kilobyte striping and has a far smaller (effective) width. We use kilobyte stripes on 12 LUNs (virtual disks) using a 4k stripe size. The disks are hardwared mirrored (on fc60, AutoRAID, va74100 etc). This means that you can use a smaller stripe size which may or may not give you performance benefits. That said I've used both & found that over 6+ disks/LUNS and they BOTH worrk fine & even out the disk activity so you do no have "hot disks" generating bottlenecks.

Regards

Tim