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Intel Matrix RAID Questions

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March 17, 2008 9:22:55 PM

Hey all,

I will soon have 4 new 500GB 7200.11 drives and plan to create a RAID out of them. I have an ASUS P5B-E motherboard (ICH8R chipset).

Originally I was just going to create a single 1TB RAID 10 volume and be done with it, but I've started pondering using matrix RAID to create a 300GB RAID 0 volume for my OS/apps, and then an 850GB RAID 10 volume for my user data.

I've done a LOT of reading on the merits of each RAID type, so I'm not really after a discussion on which is better, but more about what happens in a drive failure situation.

With the single RAID 10 volume, obviously I can just rebuild the RAID 10 and off I go again.

In the case of the mixed RAID 0/10, I'll clearly need to recreate the RAID 0 volume and reinstall my OS. The question is, what ramifications does this rebuild have on the RAID 10 volume?

According to Intel, in the case of a RAID 0 OS volume and RAID 1 data volume, you need to delete the RAID 0 volume, copy data out of your RAID 1 volume, delete the RAID 1 volume, and then create the RAID 1 volume again. I'm not keen on this at all; ie, why can't the RAID 1 volume just be rebuilt?

So, my question is, if I go with the mixed RAID 0 / 10 matrix setup, and a drive fails, can I just rebuild the RAID 10 volume, or will I need to copy all my data out and more or less start from scratch?

[Side note: Yeah, I'm aware that running a RAID 10 is no substitute for a real backup, cheers :) ]

Any help would be appreciated!
March 17, 2008 10:16:58 PM

What if you move your O/S and apps to the RAID 10 array (This would then be the "primary" array. And hey - who wants to reinstall everything after a drive failure?), and put your swap file, temp folders, scratch space, etc. on the RAID 0 array? Then if there's a failure, you just need to:
1) swap out the broken HDD
2) launch O/S
3) recreate RAID 0 array, and put your swap and temp back on it.

I've done this with RAID 5/0 matrix several times. It's a bit tricky to reboot after a disk failure with pagefile.sys being on the RAID 0, but it works (just don't let it launch too many applications on startup). Even with the RAID 0 being marked "failed" I haven't ever had to reinstall the O/S or programs. When my SATA connectors disconnected during shipping, the thing booted up with a degraded RAID 5 and no RAID 0.

Yes you'll lose a bit of space from storing your O/S and apps "twice" on RAID 10, but you'll get a performance benefit over JBOD and you'll also have less latency for retrieving small O/S and apps files scattered over your C drive than you would with RAID 0, and the added benefit of not needing to reinstall or restore from backups if a drive fails.

No, I didn't answer your question. I have the opposite configuration (O/S on RAID, data scraps on RAID 0), and I've never had to delete and recreate the RAID 5 (in your case, RAID 10) array. It always just rebuilt automatically.

You could also switch the order, so that RAID 10 is your primary RAID array, and RAID 0 is your secondary. That will put the RAID 0 closer to the disk center (slower), but you might not then have to scratch and recreate your RAID 10 on a failure. I'm guessing that the Intel requirement to rebuild comes from the location of the boot sector. But this idea depends on an ability to boot off the secondary array. I'm not sure you can do that but I think you can.

(edited for clarity)
March 18, 2008 3:55:33 PM

<quote>
According to Intel, in the case of a RAID 0 OS volume and RAID 1 data volume, you need to delete the RAID 0 volume, copy data out of your RAID 1 volume, delete the RAID 1 volume, and then create the RAID 1 volume again. I'm not keen on this at all; ie, why can't the RAID 1 volume just be rebuilt?
</quote>

I'm curious where you read this? Frankly, it's flat wrong, the RAID1 can be rebuilt. Assuming a matrix array with a RAID 1, and a RAID 0 (and booting off the RAID0), a failure of a single disk will degrade the RAID1, and fail the RAID0 (as expected). However, to recover, you can remove the failed disk, and go into the OROM (the Ctrl-I utility) and start a rebuild to a new disk. After starting the rebuild, you will next delete the RAID0 volume, and re-create it (without touching the RAID1).

There is a warning message in the OROM that states that deleting a volume will reset the disks to non-RAID. The warning message is a little unlcear, and would better be written as "deleting *ALL* volumes on an array will reset the disks to non-RAID.

Following the instructions above (I just tried them on a system), will leave you with a clean, new RAID0 volume and a rebuilding RAID1, both as part of a matrix array. You would then have to re-install to the RAID0, since the data on it is completely gone. The RAID1 will retain the original data.

<quote>
So, my question is, if I go with the mixed RAID 0 / 10 matrix setup, and a drive fails, can I just rebuild the RAID 10 volume, or will I need to copy all my data out and more or less start from scratch?
</quote>

Nope, there no need to copy the data off and bring it back for the RAID10 (of course, the usual notices/ warnings of "backup your data to be safe" still apply). A matrix array with RAID 0/10 will work the same as the array with RAID 0/1, just with 4 disks instead of 2.
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March 18, 2008 9:32:05 PM

Awesome responses everyone, thanks a lot :) 

TeraMedia: Great suggestions, I will take this into consideration and may use your method in the end if I have too much trouble with my original idea.

rockchalk: I read it over at Intel's site. Frankly, I found it hard to believe also. Thanks for the reassurance. Take a look at this: http://www.intel.com/support/chipsets/imsm/sb/CS-021015... Read the section 'Failed Hard Drive Member When the Operating System is on the RAID 0 Volume'.

I have no idea behind Intel's rationale there really, it just seems totally crazy.

I think I'll probably set up my matrix RAID sometime soon and purposely break it a few times to see how things go. Your method makes sense though rockchalk.

Cheers
September 19, 2008 8:24:34 PM

I had the configuration you described, and I could NOT rebuild the Matrix RAID 0 volume. Even after replacing the failed drive, the ICH7R version of Matrix RAID (reached with Cntrl-I) wouldn't let me recreate a initial volume, and I had couldn't reach my second Matrix RAID volume where my data was. I ended up having to delete both volumes and start over again from scratch. So as someone else said, I'd make sure the first Matrix RAID volume created is a redundant RAID level (i.e. 1, 5, or 10), and the second RAID volume as RAID 0. Alternately, you could do as I'm doing, create either one large RAID 10 volume and use Windows to partition it into 2 drives or create two Matrix RAID 10 volumes.
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