Arraydisk replacement while array is still running.

[DataCollector]

Hello.

 

Well I have some Windowssystems which habe Hardwareraid (Megaraid).
When I use hotplugging compatible Hardware (Diskcages and so on):
there I can 'unmount' a Disk in a Raidarray with redundancy, unplug the Disk and plug a new Disk in. Then the System automatically recreates the Disk.

 

unraid with paritydisks could also have the feature to replace a disk while everything is working, since the Parity has all the time the neccesary data to emulate/rebuild a missing disk.

 

But it seems unraid can not do this.

When I understand it correctly I have at least to stop the Array.

 

Just a suggestion, but would it not be easier for the user to make hotplug replacement while everything keeps running?
That way even a kind of online capacity expansion would be possible sind one could replace a smaller Disk with a bigger one (als long, as parity is always the biggest).

 

Just a suggestion, since I just made a big mistake in such a process and destroyed my parity. No problem, I have backups. But this would not have happend if the replacement would be easier. And since unraid should have all the neccesary functions to do so, it wold be nice.

With functions I mean:

- it can handle a suddenly dead drive sind it switches to emulation.

- it can detect (with hotplup capable hardware and firmware) newly inserted drives (UD registers them and one can mount them)

- it can recreate a missing Drive.

 

When I am correct it just can't combine this to one easy step (or one easy Disk Selection and push of a button).

 

Excuse my bad english. It's not my native language.

[-Daedalus]

I'm assuming this isn't that simple (fuse needs to remount things if a new block device shows up?), or it would be included already.

Having said that: +1, absolutely. 

[Hammy Havoc]

This would be nice to have. After a few disk failures lately, this would make things much easier.

[R.M.H]

This should open up the ability to have a hot spare drive. Could be something simple like the hot spare has to be the same size as the parity drive. As the parity drive has to be the same size or greater than any other drive. 

 

If your parity drive fails the hot spare becomes parity and automatically rebuilds the parity

If a data drive fails the hot spare replaces the data drive and data is rebuilt on it

 

You could then have the option of allocating 1 or a couple of slots as hot spare drives to increase the resilience of the array. Maybe even have a tick box option to set what the hot spare can be used for, parity, data or both.

[Renegade605]

I've been thinking of this recently as well as I've been doing upgrades to my server. Hot-swap / -add without stopping the array. Ideally with the following elements:

 

Add a new drive:

Since a new drive won't invalidate the parity information, simply adding one without stopping the array should be possible. Obviously Unraid must know it can't be trusted for parity information until it is zeroed out (or it can, if it's precleared in advance).

 

Remove and replace a drive:

Either for size increase or because a drive is failing, replace a drive without stopping the array. This would likely have to look like giving an option to manually offline a disk while the array is running. Gracefully stop / wait to finish all writes to the disk and switch to emulation. Then, mark a different drive as its replacement and rebuild the data on that drive.

 

Bonus points for replacement drives:

For servers that have available drive bays, mark drive B as a replacement for drive A in advance. Copy all data from A to B, and sync any ongoing writes to it. Once finished, automatically promote drive B to be the 'correct' disk in the array and unassign drive A.

 

 

I also really like hot spare functionality as described by R.M.H above.

[itimpi]

I agree these would be nice features to have but I think that the implementation problems are big enough it would be unlikely to get very high up the priority list any time soon.