[NV+ v2] 4 disks, 2 separate RAID-1 volumes?

StephenB wrote:
... Using RAID-1 doesn't eliminate the need for a backup, though it would provide another way to recover data. That could be worth the extra overhead, especially if the data is critical.

PapaBear wrote:
But not if the two volumes are different data as the member plans.

Of course it does.

If any disk in two volume set fails, you can recover the data from the other disk in the pair using off line tools on any system with a single SATA port. Basically the overhead gives you two independent copies of your data on the NAS. If you have a 4 disk RAID-5 system, you need at least 3 SATA ports on the recovery system, and the recovery is technically much more difficult.

So yes, the volume pair idea is less efficient. But if you want to be able to recover data from the original disks, it is much more practical to do that with RAID-1. I know a few IT folks who stick with RAID-1 exclusively for that reason.

You are falling into the trap of using RAID as a backup. The manuals and everyone with experience states flatly that RAID is NOT a backup solution. Separate backups must be maintained to protect against the failure when RAID will not save you. If you only lose one drive in an array and have no other problems, then that is the protection that RAID was developed for. However, in too many cases, the failure is beyond the salvage by RAID. These examples are a failed upgrade, a software glitch during some operation that creates the dreaded kernel panic error, fire, theft, hardware failure of the NAS itself. The pages of these forums are full of posts by members whose units have a problem that RAID was unable to resolve.

I ran for years with a two drive array holding all my critical and important data with only a sporadic backup. Fortunately, the only problem I had during this time was the simple failure of one drive which was easily resolved by replacing the bad drive. However, I would be remiss in recommending this as an operating plan.

PapaBear wrote:
You are falling into the trap of using RAID as a backup.

No I am not (and said as much in the earlier post).

StephenB wrote:
...Also that backups are needed...

I fully agree that RAID does not eliminate the need for backups.

All I've been saying is that if you want the capability to recover the data from your RAID array easily, then sticking with RAID-1 pairs is a good approach. It gives you more options if things go wrong. It's not the path I've taken, but I see the benefits.

StephenB wrote:
sticking with RAID-1 pairs is a good approach. It gives you more options if things go wrong.

Thanks StephenB.

Guys, didn't realize we were still dicsussing this. Yes, backups are still mandatory! I didn't mention my backup strategy in my original question because it wasn't relevant, but I see there has been speculation on my setup. I have a second NAS, I have USB drives, I have Dropbox. Despite this, I would prefer not to have to rely on my backups. Backups are more likely to get messed up than the original drives failing... I saw a scheduled backup system not execute for 3 months because something like an IP address got changed and nobody noticed. If one of my ReadyNAS drive fails, I still have all the data replicated on a 2nd drive, even stuff I changed 5 minutes earlier. It may not be quick or easy but I'm reasonably confident I can save all of that data. I will be honest -- I don't know how RAID-5 works, how 1 drive is sufficient to cover potential failure on 3 other drives. And when I have suffered one of those failures, and I am freaking out, is *not* when I want to have to learn.

PapaBear, I disagree with you on the idea of "wasted" space. All of us are dedicating a significant amount of our total storage capacity to replication/duplication/backup, it's just a matter of degree. In your setup, you have 8 disks (4 on the main NAS, 4 on the secondary) to hold 3 disks worth of data (37.5% capacity). You stated that if a drive fails in RAID-5, you need to go to your backup. So that implies that you can recover from only 1 failed drive. I have 6 disks (4 on the main NAS, 2 on the secondary) holding 2 disks worth of data (33.3% capacity). I'm OK trading that capacity loss for the benefit of being able to recover from 2 drive failures, even 3 or 4 as long as I don't get 3 fails on the same volume.

To go a little further, when I bought my first NAS around 2009, I paid $150 each for two 1.5TB drives, which was plenty of space for me at the time. Last month I decided to expand, so I bought two 3TB drives for $150 each. Thus my current primary NAS has 4.5TB of usable disk space in RAID-1, for which I paid $600. Had I gone with RAID-5, I would have had to buy 4 drives back in 2009. I would have paid $600, and had -- you guessed it -- 3x 1.5TB = 4.5TB of disk space. So it doesn't feel "wasted" to me.

I appreciate your comments and advice but wanted to eliminate the speculation over my reasoning for using RAID-1.

But, had you gone with X-Raid2, you could have put the 2x1.5 TB drives in for a total of 1.5T and now added the 2x3TB disks which would on expansion given you 2x1.5TB + 1x3TB of space for your volume for a total of 6TB of data space (1x3TB for redundancy). So, you are wasting the 1.5TB of space of one drive used for redundancy in two Raid-1 volumes that would not be used for redundancy in an X-Raid/2 volume. My volume started with 2x500GB drives in 2007 in an NV+, expanded with a third 500GB and a 750GB for a total volume of 1.5GB. I then added an NVX with 4x1TB and then replace the NV+ drives with all 1TB for a volume of 3TB. I later replace two of the 1TB drives with 3TB for a 2x1TB and 2x3TB volume with 5TB gross volume (4.5TB net).

PapaBear wrote:
...So, you are wasting the 1.5TB of space of one drive used for redundancy in two Raid-1 volumes that would not be used for redundancy in an X-Raid/2 volume...

I think you are missing his point.

illmatic fully understands the space tradeoff. At present he knows he is 33% efficient overall (6 drives between his backup and his NAS, when 2 drives are enough to hold his data w/o redundancy or backup). If he used XRAID-2, he knows he could eliminate one drive, moving to 40% efficiency.

He wants RAID-1 pairs anyway, and he doesn't view this as "wasting" anything - just like we don't view our backups as a "waste". "Waste" is a loaded word, it implies he gets no value in return. He's thought about the additional options RAID-1 gives him for recovering from future failures, and he's decided those options are worth the extra expense of one more drive.

This is really not any different from someone deciding they prefer dual redundancy over single redundancy. No one here would describe RAID-6 as "wasting" space, instead we think of it as extra protection that some people will want, but others might not.

Perhaps we should just agree to disagree, and move on?

His post here, shows that he does not understand the advantage of X-Raid2. Yes, he may prefer two Raid-1 volumes and that is fine as long as he fully understands that the second volume if set up as a backup of volume 1 will only be viable if the lost of volume 1 is due to disk failure. Any other problem will most likely take out both volumes.

illmatic wrote:

StephenB wrote: sticking with RAID-1 pairs is a good approach. It gives you more options if things go wrong. To go a little further, when I bought my first NAS around 2009, I paid $150 each for two 1.5TB drives, which was plenty of space for me at the time. Last month I decided to expand, so I bought two 3TB drives for $150 each. Thus my current primary NAS has 4.5TB of usable disk space in RAID-1, for which I paid $600. Had I gone with RAID-5, I would have had to buy 4 drives back in 2009. I would have paid $600, and had -- you guessed it -- 3x 1.5TB = 4.5TB of disk space. So it doesn't feel "wasted" to me. I appreciate your comments and advice but wanted to eliminate the speculation over my reasoning for using RAID-1.

My reply back to him was that he could have started with the two drives just as he states in 2009 and then if he had selected X-Raid2 rather than Raid1 added additional drives as he desired. If he had added the two 3TB drives has he has now, then he would actually have more storage space.

I'm not saying he has to do it this way, it's an option on the ReadyNAS units that others did not offer. I know I was glad to have it when I upgraded my volume from 4x1TB to 2x1TB + 2x3TB.

Also, as one who has lost important data in the past due to a disk problem (not even a failure) decades ago, I have been searching for a viable, reliable easy to maintain backup. When I added my second NAS and set it up as an rsync backup of my primary volume, I finally found it. I do not consider the drives in a second NAS as wasted space. I call it peace of mind.

illmatic wrote:
I appreciate Netgear's X-RAID but prefer to simply use basic RAID-1 exclusively.

illmatic wrote:
my primary concern isn't maximizing disk space (which is cheap), it is maximizing peace of mind.

illmatic wrote:
I disagree with you on the idea of "wasted" space.

PapaBear, I'm not sure how much clearer I can be here, but the ratio of (usable storage capacity) to (total disk space) is of no importance to me. That is the only "advantage" of X-RAID that I can see. I am much more concerned with recovering my data in case of a disk failure. And in this scenario, RAID-1 is superior, in my opinion.

StephenB was helpful, he pointed me to the user manual and answered the original question -- the ReadyNAS device does appear to handle 2 separate RAID-1 volumes. Your posts have not been nearly as constructive, as each one seems to repeat the idea that I am "wasting space." How about we take his advice and let it go?