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Need simple answer regarding RAID-5 expansion

R

Razerz

n00b
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Jan 8, 2007
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I want to build a combined file server and media center PC to act as a central hub in my network, and I have tough of using a RAID-5 setup with a Dell PEC 5/i or 6/i as I can find them cheap on eBay.

My question is: Is it possible to set up an initial array with three disks, and then later, without losing/deleting any data, expand the array one disk at a time up to 8 disks?

This will only be used as storage. The OS and programs will be on another disk.

I have tried searching both forums and the Internet at large, but I haven't been able to find a simple answer.

Thanks for your help.
 
I know this can be done on a number of high end cards, but I've also been told it's not a "best practice." But let someone with real world knowledge confirm that.

Basically what you are looking for is "Online Expansion" or something along those lines. From a quick search, both of those cards support it.

http://is.gd/cymDg -- dell forum post

http://is.gd/cymfp -- specifics from the manual
 
It is dependent on whether or not the controller you use supports it. Anything decent will (the two you mentioned should).
 
the perc 5 allows for raid 5 expansion, so yes, you will be able to expand while the array is online. It may take some time in order to complete the process, but it will be possible.
 
Please note that in most cases, the expansion means you degrade to RAID0 until the expansion has finished. Any Bit-Error (BER) on a disk would kill all your data. Therefore, consider expanding an existing RAID5/6, which implies restructuring ALL data, to be a risky operation.
 
Keep in mind also that if you are using RAID 5 and more than two disk go kaput, you will lose the data anyway. So the raid should not be your last line of defense against data loss. With that said, you should be able to resize the container and restore from backup if you have such means
 
During the expansion, only one disk has to have BER errors to make the expansion fail; it doesn't even require a totally failed HDD. BER is much more common to destroy your data; as it is not easy to recover from a broken/partial expansion process.

So again; don't think RAID5 protects your data; you might consider the array to be as safe as a single disk; the RAID adds some safety and removes some safety. You have more drives and another layer in the storage chain: the RAID drivers; this can lower reliability and protection, as any bug/issue of the RAID layer will now potentially destroy your data as well, or make it inaccessible without manual intervention.

A true safety net would be a backup, or a very safe RAID engine. ZFS comes to mind here, but nothing bears a TRUE and PROPER backup. Sadly, many home users don't do this because of disk costs; even though disks have become so cheap now.
 
i've expanded raid 5 with PERC5 cards, as recently as last week with three new 1TB drives.

i wouldn't give it much thought, it's easy to do.
 
Wow! Thanks for all of the quick and helpful responses!
It seems like a large RAID array isn't what I need then. I can live with one disk being destroyed/lost, but not all.
Can I use a RAID controller supporting JBOD to add several drives and keep them separated logically (is this the correct term?). I.e. if I add one disk to the controller it shows up as a single disk in Windows, if I add another, it shows up as a new disk in Windows?
That way if one disk fails, only the data on that one is lost, right?
 
Yes but as metadata is stored on the disks as well, losing one disk can cripple the filesystem and you would need special programs to recover parts of it. Generally, it doesn't work like you may think it does: "lose a disk and my Games directory disappears but the rest is still there and works".

Perhaps you can do one big RAID0 array, and use an external 2+2TB=4TB RAID0 setup as backup for your most precious things. But you have to decide between hardware costs, reliability, features, performance and ease-of-use.
 
Hmm, so there's s risk of losing everything even when using the drives as individual disks. That's not good at all.
Can a RAID controller card be used without RAID, only supply more S-ATA ports?
(Port multiplier I think it is called?)
 
I've lost drives during RAID expansion and had no problems as a result.
 
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