Raid5: Basic Questions on Migration and Expandability

[carbonti]

I had recently gone through adding a hard disk to an existing group of partitions attached to a desktop. I also took the chore of resizing some of the existing partitions while adding the new disk into the system. This seemed a laborious task in copying data across different partitons to free up the diskspace so the target partition could be resized, filesystem applied and data copied back onto it. The whole process seemed as like a cross between a bucket brigade and a chess match. There must be a better way.

To avoid this in the future, I am considering adding storage under a hardware RAID5 scenario if it is possible to do the following:

a) Boot the workstation with /boot and root a single disk and have all other files in the raid array

b) Can the raid array be expanded for storage capacity by rolling in additional hard drives into the array and rebalancing the load across the array?

c) How would data migration from /dev/sd[abcde] disks to the raid array be accomplished as I don't have the luxury of starting the raid array as a blank slate. I would like to start with a new small array and migrate data into the raid and subsequently roll each freed up disk into the raid as the data is copied off it. I can match new disks to be identical Seagate SATA150's as some of the current disks are still in production.

d) Selection of an optimal filesystem (ext2, ext3, xfs, reiserfs) for defined partitions is still a consideration in a raid storage system? The raid array just looks like a single gigantic logical disk drive, correct?

I would like to implement this with 3ware hardware - the 9000 series cards get mentioned favorably in Gentoo forums and seems linux-friendly. This workstation also serves music and video files in a home network - nothing too strenuous.

Thanks for any comments and help offered.

[ecosta]

Hi carbonti,

I'll do my best to answer your questions

a) You can have /boot and /root on a seperate disk that is out of the RAID5. That means a minimum of 4 disks. 1 For the system and the other 3 for the RAID5. I wouldn't though. Much better have it all on RAID5 and spread it over 4 disks. Remember the more disks you use the "less" space you will lose.

b) No. You can add another array but you can't add new disks to an existing array.

c) That's not possible... abd it seems more and more like you want to add hardware raid to a glorified PC which I would not bother doing. Buy a proper *real* RAID Hardware (aka a real server) or just use software RAID (mdadm). A lot cheaper and very reliable.

d) Not sure about file systems. I always use ext2/3. I hear the latest reiserfs is not so stable and I know nothing of xfs. Sorry :\

Your last comment really recomends software RAID. Remember most suposed Hardware RAID are not tru hardware RAID devices.

I would backup all my data to media *twice* and then checkit again.
Wipe the discs. Make a basic install with software RAID (check gentoo wiki... a lot of livecd installs with RAID)
Dump the old system back to the disk
make sure mdadm.conf is still there and that fstab is right. Maybe run grub again
cross your fingers and boot
Ed.
_________________
Linux user #201331
A8N-SLI Delux / AMD64 X2 3800+ / 1024 MB RAM / 5 x 250 GB SATA RAID 1/5 / ATI Radeon X700 256MB.