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Re: Workarounds for advanced RAID features in GRUB Legacy?

From: Leif W
Subject: Re: Workarounds for advanced RAID features in GRUB Legacy?
Date: Sun, 11 Sep 2005 09:01:20 -0400

From: "Tim Woodall" <address@hidden>
Sent: 2005 September 11 Sunday 06:00

I can't really see the point in mixing raid1 with anything else on a
pair of disks but even so, I'd have

Oh yeah, certainly. Sorry for the confusion. I should elaborate. Though it's veering off the GRUB topic, this background info may apply. 4 discs; 2xPATA @ 300GB, 2xSATA @ 400GB. The RAID 0 partitions are the 300GB partitions, the RAID 1 is the two RAID 0 partitions. That leaves 2xSATA discs with 100GB partitions, where I'll stuff as many OSes as I can and separate data spaces, RAID 1 when I can. :-)

At the least, I'm looking for two non-raided winxp installs (one on each disc). If winxp can't play ball with the grown ups then it can go without redundancy. ;-) Besides it has a higher probability of breaking than my hardware, so I'd just be mirroring the same broken OS. They often require a reformat and reinstall after 6-12 months anyways. Then I'd like two installs of Linux, both RAID1, just incase I really mess one up and need something ready to go in a hurry. RAID 1 will mirror the user error. A separate, unmounted partition will not. Two linux and two windows swap partitions (one on each disc). And two data partitions per disc, Linux mirrored (2/3 remaining space), and WinXP just with two separate partitions, so that data (like software projects) doesn't live and die with the distribution.

Now, there may be things I overlooked, it's a work in progress, a hobby I've been nudging along for some time now.

I don't run WinXP but this looks like a limitation in WinXP. If WinXP
requires you to raid the entire disk then that is what you are going to
have to do for WinXP.

Well, I'm just basing my experience on the stock utilities in WinXP, and the disc management console didn't give me an option to select partitions to be part of a RAID array. With the drivers and utilities for the SiI3112 chipset, WinXP can do only RAID 0 or RAID 1, only on SATA, and only the entire disc. And it will happily attempt to make a RAID1 array even though it is running from the drive! It's the computer equivalent of watching something so mind bogglingly stupid like Jack.*s that you can only laugh. Actually I might end up keeping that OS on another system with very similar hardware.

I suspect, however, that if you raid the whole
disk but then in linux treat the end of each disk as non-raid and then
run software raid in linux it will still all work correctly. (for raid1
at least although you definitely want to check that rebuilding the
mirror in windows doesn't break the linux raid)

If I had more time and energy I'd be curious to see the results myself. Probably worth a good laugh at worst if it fails miserably, and at best utter astonishment if nothing broke.

It's not unusual when a disk fails, expecially IDE disks, for it to
crash the machine hard so you are going to have to reboot. And it's also not unusual for the bios to crash if there is a failed disk meaning you can't boot until you unplug the failed disk. (Almost all my experiences of failed disks have either been bad sectors (which hopefully raid1 will compensate for) or failed to start after a shutdown (where bios hanging isn't uncommon) - but it's not like I'm in a datacentre (which would all

My experience was most likely due to thermal issues. Despite being concerned at the volume (and rotational torque ;) of my case due to the 15 or so fans and specialized heat sinks, several discs died during some hot weather with no A/C, and I didn't chalk it up to coincidence. The system didn't crash hard. The discs would start knocking audibly, and access times crawled. After a while it was recognized by the BIOS but not the OS, and then no longer recognized by the BIOS, like nothing was there. Air flow and temperature monitoring are more important to me now, so is some redundancy and external backups, so I can at least limp along.

If you are very lucky the machine will stay up, mdadm will flag the disk
bad and you will get a message. A bit less lucky and the machine will
crash but a power cycle will be sufficient. Worst case, you will have to
unplug the cable from the failed disk in order to get everything up
again. Once you have the new disk you can install inplace of the failed
disk and rebuild the raid (or have another spare)

Well if that's the way it is, I can understand. So long as it's not something that can be configured away.

Thanks again for the commentary.


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