What do I need to know before swapping in a new drive?

fearless_fool wrote:
Hot or cold swap: which is safer? Note that my system gets hung during FSCK on startup (so I have to do the 'hold the power button for 5 seconds on powerup to skip FSCK' to get past that), so that *might* argue for hot swapping. Comments?

The benefit of hot-swap is that the NAS detects the new disk insertion directly, and starts the resync process.

Of course there are times when you don't want the disk wiped and rebuilt - for instance if you are removing it so you can run a diagnostic on it. In those cases you should always cold-swap.

If you are inserting an unformatted disk, both should work (as the NAS should discover it is unformatted when it starts up). Though still, I think hot-swap is generally the best way to go when adding/replacing disks in the array.

fearless_fool wrote:
The SMART report says that Channel 3 is dying. Just to make perfectly sure: are the disks labelled 1-2-3-4 left to right? I don't want to yank the wrong one.

It would be nice if there was a label. One thing to add to vandermerwe's reply: If for some reason you accidentally remove the wrong disk, the best thing to do is immediately power down the NAS, and cold-insert it. You don't want the system to rebuild the array. Also, if you do just stick it back in (hot-insert) be sure you wait until the resync is complete before proceeding. The NAS can only rebuild one disk at a time. Doing two at once will destroy the volume.

fearless_fool wrote:
StephenB and others recommend backing up the ReadyNAS before attempting a disk swap. Ignoring the fact that this *is* my backup system, how and where would you back up 2TB of data? I"m concerned that by the time I procure any necessary gear and to a backup, the drive will have failed completely. My gut says that I should install the new disk sooner than later. What would you do?

A couple of comments here:
(a) Anyone who cares about their data should develop a backup strategy that protects it against the various failure scenarios. There is of course a cost, so you might chose not to protect it against every possibility. Loss of data on one device is reasonably common. Sometimes failure of the backup device isn't detected until you attempt to recover the data from it. So two failures are more likely than you might think. Then there is a disaster recovery - lightening, fire, theft, etc - something that destroys all your devices.

My strategy is set up to protect against two failures (primary device and the primary backup), and also the disaster scenario. Basically I keep a primary and a secondary backup on site, and use crashplan for the disaster recovery. These are always recent, so when something does fail, I can act immediately. Possibly overkill, but I prefer a "belt and suspenders" approach (and learned the hard way about needing a secondary backup some years ago).

(b) You are correct in thinking that delay increases the possibility of data loss in the NAS. You have 4 disks in the NAS, probably all are about the same age. Another one could be start failing (or might even be already silently failing). The volume is more vulnerable because you have lost redundancy.

So if your NAS is only used for backup, and is not used for primary storage, then I would probably risk doing the disk insertion immediately w/o making a secondary backup. That assumes your primary storage (pc, whatever) is running normally and is not at risk of failure - something I would double-check before proceeding. If the NAS is used for some primary storage, then I would back that stuff up first, and then do the new disk insertion.

Then perhaps after you are up and running again, you can revisit the overall backup plan, and make any changes you think are needed.

EDIT: I just wanted to add that 2 TB of data can easily be backed up on one USB drive. It gets more complicated when you have > 4 TB, as then the backup won't fit on a single disk. One approach to that problem (which you don't have at this point) is back up to another NAS.