confusion about hardware raid

goldfita · n00b Joined: 27 Nov 2005 Posts: 40

Hello,

I'm trying to set up hardware raid with gentoo. I have 5 scsi disks and an adaptec aaa-130u2 adaptor. I believe there is no linux support for this device but also that you can use the generic aic7xxx and it will work just fine. After I set up the array and boot from the gentoo install cd, there are 5 devices in the dev directory (sda, sdb, sdc, sdd, sde). Should I be seeing only one logical device? Do I need to do something else.

There is a lot of info on software raid. This post would seem to indicate I should use software raid. But I'm not sure.

https://forums.gentoo.org/viewtopic-t-401731-highlight-raid.html

Thank for your help!

jmbsvicetto · Posted: Sun Nov 27, 2005 12:45 am Post subject:

Hi and welcome to the forums.
If you had support for hardware raid, you would only see one drive, not five. Have you tried using the Adaptec RAID aacraid? However, I can't tell you if it will support your card.
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tgh · Apprentice Joined: 05 Oct 2005 Posts: 222

My personal preference is to go with Software RAID over hardware RAID in linux. Mostly because:

- lots of flexibility in how you configure the disks
- ability to monitor arrays in linux without special software
- reuse code from other's who monitor their /proc/mdstat status
- no dependency on particular hardware
- easy to move software RAID disks to other controllers in the system

The biggest fear that I have when running on a particular brand of hardware RAID is that the card will get fried and I'll have to go hunting for a new controller that is compatible. (The expensive answer, of course, is to buy (3) controllers. Install one, keep one on-site as a spare and keep the other one off-site as a backup spare.) This gets easier if you have multiple machines that all use the same RAID card, then you might only need 2 spares for every dozen machines. But when every machine you buy is unique, it's worrisome.

Granted, I have't done software RAID on top of SCSI yet.

But to give an example of disk portability: While troubleshooting an issue with my AMD64 unit, I was installing/uninstalling numerous add-in IDE cards. Moving the (2) RAID1 disks around to different ports in the system, etc. The mdadm software RAID simply didn't care when drive identifiers changed, it used the UUIDs on the individual components of the RAID arrays and assembled them into the proper RAID volumes. (I eventually went back after I was done and touched up mdadm.conf to reflect the proper drive identifiers, mostly so I wouldn't confuse myself a few years from now.)

I'm sure other folks have opinions that hardware RAID is better.

goldfita · n00b Joined: 27 Nov 2005 Posts: 40

Well it looks like I'll have to use software raid if gentoo doesn't work with my controller. The only problem I have with that is I have to do the setup work and it will eat a lot of cpu time.

Is aacraid an alternative raid controller module?

goldfita · n00b Joined: 27 Nov 2005 Posts: 40

I went ahead and did software raid since gentoo was seeing 5 drives. After the first failed attempt, everything went smoothly, except that for some reason the last hard disk does not appear in /dev on the mounted raid drive (but it did appear in the livecd environment). So I couldn't install a boot image using grub on that last drive. But looking at mdstat, all 5 drives appear to be working in a raid. I also couldn't shut down without forcing. Reboot couldn't find /dev/initctl.

After reboot, the boot screen did not disply at all (but I know it was in boot). Once it booted, some info was quickly displayed and then replaced by barely readable text. One line appeared to say something about not being able to find /dev/md2, which is the root mount. So I'm not sure what's wrong there. The other really frustrating thing is, in order to mount my raid drive from the boot cd, I first have to set up raid, which means typing in the entire raidtab file each time until I figure out what the problem is. I think I'll burn the file to a disk (no floppy drive). Is there another way I can deal with this?

jmbsvicetto · Posted: Mon Nov 28, 2005 7:54 pm Post subject:

Your problem with the 5th SCSI disk is caused by the Live-cd only having devices for /dev/sda up to /dev/sdd. You can solve that, by doing the following outside the chroot.

tgh · Apprentice Joined: 05 Oct 2005 Posts: 222

Semi-OT... but why is it needed to use a raidtab file instead of using mdadm and relying on the RAID superblocks that get written in the partitions? I've been able to mount RAID systems from the LiveCD using:

# modprobe md
# modprobe raid1
# for i in 0 1 2 3; do mknod /dev/md$i b 9 $i; done
# mdadm --assemble /dev/md0 /dev/hda1 /dev/hdc1
# mdadm --assemble /dev/md1 /dev/hda2 /dev/hdc3
# mdadm --assemble /dev/md2 /dev/hda2 /dev/hdc3

No need for me to type in a raidtab file at all. (And I can use the output of mdadm --detail --scan, dumped into /etc/mdadm.conf as a backup configuration. Creating the disks was done using the "--create" option of mdadm.)

(maybe this question belongs in a new thread...)

goldfita · n00b Joined: 27 Nov 2005 Posts: 40

Thanks, I'll try that to mount.

linuxtuxhellsinki · l33t Joined: 15 Nov 2004 Posts: 700 Location: Hellsinki

goldfita · n00b Joined: 27 Nov 2005 Posts: 40

Those last few posts were helpful. I think I'm almost there. What I'm seeing when I try to boot is this.

md: Autodetect RAID
...
Cannot open root "md2" or unknown-block (0,0)
Please append correct "root=" boot option
VFS: Unable to mount root fs on unknown-block (0,0)

Any suggestions? md2 is where I'm mounting root.

tgh · Apprentice Joined: 05 Oct 2005 Posts: 222

Please post your grub.conf, here's an example of what my grub.conf looks like for a 2-disk PATA RAID (md0 is /boot, md1 is swap, md2 is root, md3 is LVM2 using the rest of the disk on my systems):

augury · l33t Joined: 22 May 2004 Posts: 722 Location: philadelphia

mdadm is for software raid, you set up raid in the cards bios. they appear as disks. GL

augury · l33t Joined: 22 May 2004 Posts: 722 Location: philadelphia

these disks are already on a scsi and w/out raid theres no telling weather or not they will act as a single channel or dual channel. the card is going to inflict overhead that will hurt a software raid.

goldfita · n00b Joined: 27 Nov 2005 Posts: 40

It turns out I was missing some raid support in the kernel. I can boot now. The only problem is, it's unable to mount the boot partition. It fails on fsck - says that it's not a valid ext2 partition and it can't be repaired. I tried mounting it myself and had the same problem. I tried using mdadm to recreate md0 but that didn't work.

However, I have no trouble creating md0 from the livecd and mounting boot. So it is a valid partition. In my fstab I have /boot labled as ext2 (on the hard disk boot). I'm pretty sure it is ext2. Is there any way I can check?

goldfita · n00b Joined: 27 Nov 2005 Posts: 40

I've gotten everything working.

When I reboot, it tells me it can't shut down the raid drives, but restarts anyway. Halt seems to work. Is this something I should be worried about?