Can the drives in a RAID 1 array be rotated?
As a follow-up to my question https://superuser.com/questions/247070/disaster-recovery-backup-of-files-photos-for-personal-use, it sounds like for personal disaster-safe backup, multiple rotated hard drives is the way to go.
One of the answers suggested a NAS RAID setup, so after some searching I found a very affordable product that looks really cool, the D-Link 2-bay network storage enclosure.
However, this NAS has some pretty cool features that I would love to use and not just lock away in a box, such as becoming my streaming location for Xbox, etc. It is a 2-bay enclosure, so what I am thinking is that I can buy 3 drives, and keep two of them in the NAS, and one in the fire-proof safe. I would rotate them weekly.
Is this possible with a RAID-1 array? Would it have to wipe the whole drive to rebuild it every time? Does the rebuilding happen automatically? And last question, if it does have to rebuild the whole partition on the drive every time, would this excessive writing reduce drive life?
Yes, this is possible, but not the best possible idea. A far better thing to do would be to purchase a NAS that allows you to connect an external hard drive to write backups to. This way you could connect a drive via USB (or eSATA, or whatever), your NAS could back itself up to the drive, then you could disconnect the external drive again until your next backup.
However, if you're hell-bent on attempting to rotate drives in and out of the array, the safest way to do this is to use the following procedure:
- Shut down the NAS
- Remove the drive you want to store
- Start up the NAS
- If your NAS does not allow for hot-swapping drives: Shut down the NAS again
- Insert the new drive
- If you shut down the NAS in step 4: Start up the NAS
- Initiate the RAID rebuild, if it's not possible to do automatically.
Shutting down the NAS in the first step is important to ensure that all your data is consistent.
Starting it back up is vital to ensuring that your rebuild goes correctly. This is what allows your NAS to know that a drive is missing, your RAID is "degraded", and most importantly -- which drive is left. If you put in the replacement drive before the NAS knows this, there's a possibility that it won't know which drive contains the correct data. Remember: The replacement drive you've put in was a member of the same RAID array too. Unless the NAS has some sort of special metadata to let it know which one is "newer" and therefore the "real" drive, it may not know what to do.
I like the D-Link NAS; just bought one a few weeks ago and set it up RAID 1 just like you as well.
It is my understanding that the D-Link NAS RAID 1 operates the primary drive and mirrors to the second in this way; I also notice that apon read it appears it reads off of both drives for speed; however this may be incorrect and it may just be checking for consistancy.
RAID 1 is therefor setup that if either of the drives fail; the second (hopefully working drive) is then used as the primary, until the failling drive is replaced; where by the controller writes all the good info (ie 2nd drive) to the new unformatted or 'other' drive (drive 3 or perhaps if you fixed drive 1 say with SpinRite you could use that). This process would happen automatically with the controller... just don't move drives around until the data is written to the new drive other wise it is possible the controller could loose track and reformate your old drive and your data is gone!
This says to me that yes you could swap in and out 3 or 4 or more drives for additional redundancy as you cannot use a second NAS in any RAID config as of yet (you would need a Network RAID controller; not sure if this exists) and the NAS would just make sure the new drive you inserted is mirrored the same as it's "Primary"
Key notes:
- don't remove a drive while Writing/ avoid while reading
- HDD get writen to and read from time and time again on a regular computer usage; think every time you visit a webpage; read email; download; save a file; if you are using one for back-up it is prettymuch 'almost' safe to assume it's being used less than your normal CPU HDD(s) so the life expectancy is higher
- that's why you are using multiple drives for the redundancy so that if one fails you have backups... not sure that reformat or full data writing lessens the life cycle; it will take longer and longer as your data adds up; You'll have to experiment but a Disk is only magnetized info so putting it on (0's and 1's) and taking it off is what it is designed for.
- Nice feature with the D-link NAS is that it allows you to enter the disk 'shutdown' time for non use which is nice for back-ups and occasional use as it is still available on the Network all the time but the Drives don't have to be spinning if you not using them!