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Disc failure during expansion
Hi all. I have been running a ReadyNAS with 3 drives in for a while, (2+2+4 Gig respectively). I ended up with 3.6TB of capacity, and hit 80%+ full the other day. Accordingly, I put an 8Gig dr...
robinwatts wrote:
If I had an array with 4+8+8, could I safely add another 4TB drive later to get it to the maximum 16?
The usual guidance is that you can only add 8 TB (or bigger). Taking the expansion limits into account, that means upgrading the 4 TB to 8 TB.
Some experiments posted here show that OS-6 NAS would let you add a 4 TB (since there is a 4 TB already in the array). However, I don't know if OS 5 will allow that (though it is technically possible).
Under the covers, a 4+8+8 setup has two RAID groups - a 3x4TB RAID-5 group that covers all drives, and a 2x4 RAID-1 group that covers the two larger drives. These are assembled into one volume.
Adding a 2 TB drive requires that the 3x4TB group be split into two 3x2TB groups (followed by adding the new drive to one of those groups). XRAID won't split an existing group that way (and I don't think it can be done easily w/o data loss).
The only ways to restore redundancy are to
- add another disk. (either 2 TB or 8 TB).
- or do a factory reset and restore data from backup.
I do recommend creating/updating your backup in this situation, since another disk failure will result in loss of all your data.
Your disk setup does waste space (with single redundancy the two largest disks should be the same size).
If I add another disc (say, another 8TB one), will that give me the expected amount of space? (i.e. at least 10TB redundant storage)?
Thanks.
The rule for single-redundancy XRAID (what you have) is "sum the disks and subract the largest".
So with 2TB + 4TB + 8TB + 8 TB you'll get 14 TB of redundant storage. The NAS reports TiB, so it will say ~12.7. (TB: 1000*1000*1000*1000 bytes; TiB:1024*1024*1024*1024 bytes).
If your 2 TB drive hadn't failed, you'd have had 2TB + 2 TB + 4 TB + 8 TB. That would have given you 8 TB (~7.3 TiB).
Thanks for that useful rule.
I've ordered a new 8TB drive.
I just want to be clear though - if I just power the array down, insert that new drive and power it back up, that'll give me the optimum setup?
The alternative (of connecting the new drive by USB, copying all the data across to it, factory resetting the NAS with the 3 drives I've already got, copying the data back on and THEN adding the 8TB drive) seems like a lot more faff...
Thanks.
robinwatts wrote:
I just want to be clear though - if I just power the array down, insert that new drive and power it back up, that'll give me the optimum setup?
You should be able to hot-insert the new drive into the failed drives slot. No need to power down, and there should be no need for a factory reset.
It is a good idea to back up the data though, just in case. RAID is a good thing, but it's not enough to keep your data safe (even when the array isn't degraded).
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