topic Re: RAID 0+1 in Operating System - HP-UX

RAID 0+1

PVR — Tue, 05 Jul 2005 09:49:33 GMT

Hi !

Please let me know whether I can create RAID 0+1 and RAID 1+0using LVM ?

Thanks
PVR

Re: RAID 0+1

Pete Randall — Tue, 05 Jul 2005 09:53:05 GMT

With the optional MirrorDisk/UX product, you can mirror logical volumes and LVM also allows you to do extent based striping so yes, you can approximate RAID 0+1 but it's not really the same as having a true RAID hardware solution.

Pete

Re: RAID 0+1

PVR — Tue, 05 Jul 2005 09:59:13 GMT

Is it like.........

Create the stripes first and mirror it using lvextend ?

Is there any extra steps to be executed to configure the same ?

If anybody has some handson experience, please help

Re: RAID 0+1

Pete Randall — Tue, 05 Jul 2005 10:05:50 GMT

I've never done LVM striping but yes, I would think that you would have to create the striped logical volumes and then mirror them. That's the way MirrorDisk works: create the LV, then mirror it with lvextend.

Pete

Re: RAID 0+1

saju_2 — Tue, 05 Jul 2005 10:17:05 GMT

HI PVR

In almost all servers, the root disk is striped and mirrored (If resources are available).

First check whether mirrordisk UX is available.

First create the LVOL with lvcreate command with -i . So the LV will be striped to that many number of PVs. Once this is done do a lvextend -m 1 . This will do the mirror copy

Regards
CS

Re: RAID 0+1

Devender Khatana — Tue, 05 Jul 2005 10:33:46 GMT

Hi Pramod,

Important to note here is across how many disk you want to create this LVOL. Suppose if you create it across two with stripping consuming half of the disk space across both. Then during mirror there is a possibility that your second copy of mirror could be lying on the balance half space on these two disks itself. This way allthough your striping is there but you have multiple copies of data across same physical volumes.

So take atleast 4 disks of same sizes to achive this & then use distributed allocation.

HTH,
Devender

Re: RAID 0+1

DCE — Tue, 05 Jul 2005 12:31:32 GMT

I believe therenow is a -D option on lvcreate that allows you create stripes that can be mirrored. Do a man on lvcreate for more info

Re: RAID 0+1

A. Clay Stephenson — Tue, 05 Jul 2005 13:11:21 GMT

Yes, it is possible with LVM to setup extent-based striping with mirroring; however, I have yet to measure any performance increase with this configuration. The problem is that the smallest possible physical extent (1MB) is much to large a chunk to stripe efficiently. Moreover, using 1MB PE's limits the maximum size of physical volumes quite severely. Ideally, your stripe size needs to be 64k to no more than 256k to spread the i/o
among the disks.