I have been using my ReadyNAS Pro Business with two 1TB drives in X-RAID2 for three years now. I have kept a third 1TB drive as a "cold" spare. In the past three years, both of my 1TB hard drives developed errors, and I had to send them to Seagate for replacement. I used the "cold" spare to rebuild the RAID so that while Seagate processes the RMA, I don't run my ReadyNAS in the degraded mode on just one hard drive. This strategy worked well for me for the past three years. Finally, I got to the point where I started getting low on storage space with 1TB redundant storage. So, I had a choice of either adding my cold spare as a third HD to the X-RAID2 volume, and thus doubling the redundant storage but leaving myself without a cold spare or buying another HD for that purpose and continuing to keep one HD outside of the ReadyNAS as a cold spare. I decided to go with the latter and purchased a fourth 1TB HD. After that HD arrived, I did the following:
1. Powered down the ReadyNAS and took Disk1 out to keep it as a backup in case something goes wrong with the volume expansion.
2. Powered up ReadyNAS, made sure everything was working fine (share access) and added a new 1TB HD as Disk1. At this point, X-RAID2 started rebuilding the redundant volume, which took 4.5 hours.
3. Once the volume became redundant, I added another blank 1TB HD as Disk3. X-RAID2 started restriping the volume, which took about 7 hours. I went to bed while it was still doing the restriping, and when I woke up, my volume had expanded to the size almost double that of the previous size.
I noticed that I now have an option that lets me choose between: A. Next added drive will be used to expand volume, or B. Next added drive will be used to add dual redundancy.
I was not aware that dual redundancy was an option with X-RAID2. I thought this was only an option with Flex RAID, and it had to be selected during the RAID initialization phase. It appears that this option has recently been added to X-RAID2, and it does not require moving all the existing data off the NAS and re-initializing the RAID with this option.
I am a little apprehensive about choosing this option and adding my fourth 1TB HD as a hot spare, using the dual redundancy option that X-RAID2 now offers. If something goes wrong with the migration from the single redundancy to the dual redundancy, I will have no backup , and all of my data may be lost. Of course, I should probably start making backups to external HDs and take them offsite. There are now 1TB 2.5" drives available for $120, so I can get two of those, put them in USB enclosure, and rotate them once a week, making a backup during a weekend and taking the drive to work with me. I can use such a backup to restore my data if the X-RAID2 migration to dual redundancy goes awry.
So, even if I take this precaution and migrate to dual redundancy with a hot spare, is this strategy any better than having a cold spare outside the ReadyNAS? The hot spare will be powered up and spinning even though it will not be part of the volume, right? So, it will be incrementing hours, which will shorten its lifespan compared to it sitting in a box outside the NAS.
Dual redundancy is NOT a hot spare. The hot spare option is only available with Flex-Raid, not X-Raid2. With dual redundancy, your array will be able to survive a dual hard drive failure. You commented that you have had a couple of single drive failures, yet your array survived intact. Had you experienced a second drive failure before you replaced the failed drive your array would have seriously compromised if not lost. The dual redundancy is designed to protect against this.
Dual Redundancy is only available with X-Raid2 with at least four drives installed in a 6 bay or greater ReadyNAS.
But of course keeping a current and complete backup is always a good idea. One can never know if a disaster is going to strike your Pro. (Fire, theft, tornado, hurricane, equipment failure, etc). In such a situation your separate current and complete backup would be your recourse. I used to keep my critical files on WD passport drives, and keep the most current in my desk at work and the other ready to update over the weekend. On Monday, I would then swap the drives. Today, I don't have a desk at work since I am retired, so the one is in my safe deposit box instead, and that is in addition to a second backup ReadyNAS.
Just noticed on a post in another thread, an experienced member was pointing out that the transition from single to dual redundancy can only be done on-line (without a factory default) if you have an open drive bay which allows an expansion to take place. I would not anticipate any problems, but like any expansion, there is a stress on the drives and a good backup is always a good idea.
