Software Raid 5 and Online Capacity Expansion

[fletch76]

Does anyone know if any of the following OS's support online capacity expansion (AKA dynamic array expansion) if I do software raid 5? That is, once I have a raid 5 array with data on it, can additional disks be added to the array without wiping all the data first?

1. Windows 2000
2. Windows 2003
3. Windows XP...yes, XP can do Raid 5 -> http://www6.tomshardware.com/storage/20041119/index.html

 

[Nothinman]

3. Windows XP...yes, XP can do Raid 5 -> http://www6.tomshardware.com/storage/20041119/index.html

Sure, if you void your warranty and do something stupid like patch system binaries.

And in any case I wouldn't trust any expansion without a full backup, hardware or software on any OS.

 

[spyordie007]

Once the array is built changes are not supported by the OS.

And like Nothingman said; you better have good backups before trying anything like that...

 

[fletch76]

So maybe hardware Raid 5 is the way to go, since some of the cards seem to support online capacity expansion...I'm pretty sure that Linux software raid supports OCE too. Maybe I'll do some testing with Linux (and Windows, for that matter) before shelling out the $ for a hardware card.

 

[Nothinman]

Linux LVM should do on-line expansion, but as I said I still wouldn't do it without a known-good backup.

 

[Smilin]

Hardware Raid5 is always the way to go. Software Raid is *great* for Raid 0,1 but Raid5 has too much CPU overhead.

If your Raid hardware supports it you can easily add drives to an existing array without rebuilding it and without having to resort to your backups (Which you have anyway right?). All of the OSs mentioned above natively support expanding a data partition into the new space, just use diskpart.exe.

Avoid Tom and his cronies. Sure you can edit your binaries, then fool with your dllcache to prevent Windows from repairing itself, but the first time you apply an update that touches one of those files you're going to have trouble. Quite often Tom is a complete idiot. Just because you can modify your toaster into a Linux SAN doesn't mean you should.

 

[fletch76]

First off, thanks for the info. This will be a media server only, therefore the CPU utilization associated with Raid 5 doesn't bother me (I won't be running any apps whatsoever on the server). You've talked me out of using XP, but I'm still leaning towards Windows 2000 or 2003, which have Raid 5 capability without the need to edit any binaries, etc. Just so I'm clear, using diskpart.exe to expand the partition doesn't wipe the data on the existing array, right? A full backup of all my media probably isn't feasable or affordable at this point, but it's mostly DVD and CD rips, which are re-rippable, admittedly I DON'T want to have to re-rip b/c it was an incredibly time consuming process. I'd go the hardware raid 5 route, however, I can't seem to find an affordable 8+ channel PATA card (NOT SATA, since I have PATA drives that I intend to use already) that supports online capacity expansion. Basically, I'm trying to balance a cost-effective, reliable, and expandable (down the road) media storage solution...so I'm open to other suggestions. If I could trust that expanding a software raid 5 array with a new disk as the need arises won't wipe out my data, this would be the ideal solution IMO, but it doesn't sound like I should make this assumption...

 

[Smilin]

Where diskpart comes in: If your raid 5 array supports expansion it will add the new disk as additional empty space on the existing logical volume. If you have the volume in two partitions, OS & Data you can expand the data partition into the new unpartitioned space without losing any data.

Prerequisites: Must be a basic disk, can't expand the boot partition, the extra space must be immediately next to the partition you wish to expand.

Where it won't do you any good: Software raid since it can't be expanded. Hardware raid that doesn't support expansion of the array to begin with.

If uptime is not a big concern you might skip Raid 5 altogether. For a media server it makes a difference how many clients are hitting it at once. Raid 5 has some performance benifits but if only a few people are hitting at once then spanned disks/JBOD will probably work just fine.

Obviously spanned disks are quite easy to expand without rebuilding/restoring.

Another option: Put a hardware raid 5 together. When it comes time to expand, simply create an additional raid 5 array, raid 1 array (or even some simple volumes if you don't mind losing the redundancy). Then span the logical raid volume over onto the new disks via software.

Another option: Put a hardware raid 5 together, when it comes time to expand simply add new disks to mount points in the original drive's folder structure. If one of the new drives blows you simply lose the contents of that folder and not the whole spanned volume.


FYI, I've got a 4 channel Raid 5 PATA controller gathering dust in the original box. PM me if you want it. I'll sell it real cheap, say $75 - I'll cover shipping. It supports dynamic expansion. Details: http://www.promise.com/product/product_....asp?segment=RAID%20HBAs&product_id=94