Software or Hardware RAID

[priithansen]

Hello

I'm soon faced with a challenge to install Zentyal on a DELL PE T110 QCX which as war as I know has RAID included in hardware.

The configuration would be Two 500GB drives in RAID1 mirror and one 1000GB for rsync incremental backup.

So my question is would it be smarter to use software or hardware raid?

And after my test istall on a virtual machine with two scsi drives with default install Zentyal didn't want to recognize my second drive. Should I select advanced install or do something during the Installation procedure to make the extra drives recognized?

Would also like to thank for the supper product that is Zentyal.

[FutureTechSys]

This is one of those "opinion" things.  Personally, I would always go with hardware RAID, especially if you have a true raid controller.

If it's not recognizing your second drive, it's probably a driver issue.  Do some googling rather than Zentyal though, search for something like "ubuntu not recognizing scsi drive" or something along those lines.

You're pretty much guaranteed to be doing some command line stuff, and quite a few reboots.

[priithansen]

Thank You for the advice.

With true hardware raid the two drives appear for operation system as one right?

I don't think it would be a driver issue as the two vmware drives must be identical.
Maybe my question should have been what's the right way to install Zentyal with multiple harddrives?
Should it recognize them automatically or is there something I should keep an eye out during the install.

Thanks again.

[FutureTechSys]

Yes, true raid will make it show as one drive.

It should definitely recognize them automatically.  It will ask you how you want to partition, format, etc.

I'm not great at troubleshooting hardware/drivers (not on linux anyway) so I'll leave that to the experts, but I know with SCSI even with Windows installs sometimes they are troublesome.

[priithansen]

Huh after a night of messing and following every ubuntu tutorial i can find about raid software raid install I got it working but not the tutorial way.

All the tutorials seem to suggest that in the installer partitioner i should make all my swap /home etc partition identical on both drives make the usage type "volume for RAID" and then set up a raid for each pair of partitions.

Using that the system installs fine but after reboot hangs at login. Using
cat /proc/mdstat   i see that md0 and md1 have only 1 drive live and md2 that is the /home partition is dong a sync.


So the only solution I got to work is this:

1. delete all partitions on drives so only free space is left
2. make software raid out of two drives free space
3. create  volume group from /dev/md0
4 create logical volumes onto the volume group

So what I end up looks like this http://priithansen.com/raid.jpg

Could anyone tell me if it's ok or a bad idea.

[FutureTechSys]

Looks OK to me.  If it were me though, I'd purposesly break it and try and recover, and see that you are in fact able to rebuild the array, before you start putting data on there.

[Sam Graf]

I'm not an expert by any means, but I'm not sure that mixing RAID and LVM is the right approach. I would think that generally it's one or the other. In my own use of software RAID, I don't use LVM.

My first attempt at setting up Ubuntu software RAID was guided by this tutorial:

http://advosys.ca/viewpoints/2007/04/setting-up-software-raid-in-ubuntu-server/

If the machine is already equipped with true hardware RAID (in contrast to so called fake RAID), I personally would opt to use that. In the case of hardware RAID, the installation appears to use a single disk, and the hardware handles the actually arrays. Zentyal will report that RAID is not in use in the case of hardware RAID, but that's OK. In the case of Ubuntu software RAID, Zentyal reports the status of the arrays.

[FutureTechSys]

Agreed again on the hardware - if the hardware raid is set up properly, Zentyal/Linux/Mac/Windows/Whatever will see it as just one drive, although some may be able to see the individual drives as well.

My machines have SSD drives for the boot drive, a single SATA drive for data, and use SpiderOak for online backup.  No tapes, no raid, no problem.  Check out my sig if you want to see what I mean and test it out - its a pretty nice GUI.  RAID is great if you lose a drive, but not if the building burns down - you need offsite backup for that.

[priithansen]

Damn apparently I partied too soon
If i remove any of the drives it gives this.
I would have used the non lvm method of doing things but with that I didn't get the system booting.

All out of ideas here how to go forward.

[Sam Graf]

In the simplest RAID1 case (a / partition and a swap partition residing across two physical drives), and with Ubuntu Server 10.04 software RAID specifically configured to boot a degraded array (it's a setup option), it should survive a replaced drive. I don't know about trying to boot from a single drive even on a correctly configured system.

In your case, you don't have a bootable RAID partition, as far as I can tell.

[Josep]

Quick comment here: having a RAID as the system drive doesn't seem a good idea. The purpose of a RAID system is to withstand a drive failure. But ... if one of the drives fails, you would need a system to rebuild it, right? Now, if your system is on that RAID, you can't repair it if it fails ...
The FutureTechSys configuration seems quite reasonable: a small drive for the system and a large storage for data (be it a single drive or a RAID). If the RAID needs to be rebuilt, you still have the system drive.

[FutureTechSys]

Depends on the RAID level.  I don't know the numbers off the top of my head, but there's one that has the ability to lose a drive in the array and still boot.

Personally, if you're going to use a free OS, there's no point in putting thousands of dollars worth of RAID stuff on it.  And as I said a RAID array won't survive a fire!

[priithansen]

Well RAID 1 mirrors data on to both drives so one drive failing shouldn't stop the system from booting up. Tried that with vmware and two drives and everything works so I'm thinking it's some bad md superblock left from earlier tests.

Doing dd if=/dev/zero of=/dev/sdX bs=1M on all drives to zero them out and will try again.

[priithansen]

Finally go the RAID working and wanted to share the solution maybe it will help someone with a similar trouble.

1) Made the LVM partition a little bit smaller then the whole drive. Apparently when the partition is the full size of the drive the system can confuse the version 00.90 md superblock belonging to both the drive and the partition.

2) The other thing I'm not sure if it was related or not was that mdadm uses servers host name for itentifying the drives. It writes the name into md superblock. Problem however rises when computer boots and initramfs has no idea what the hostname is so it gives out <null>.
My solution was to write the hostname into /etc/mdadm/mdadm.conf and do a update-initramfs -u.

Now the RAID works just fine. Only thing is that after booting with a missing drive and then reconnecting it doesn't automatically fix the array I need to manually add the drive back to array and mdadm rebuilds it. Could be that this is not a bug, wouldn't want a corrupted drive somehow connecting itself back to the RAID but I thing with vmware and SCSI drives it indeed reassembled the RAID automatically.