Can TS-4xx Support two RAID1 pairs?

[storageneeded]

Can the 4-bay units be initially configured with a single pair of RAID1 drives (2 bays still empty) and then later add a second RAID1 pair as a new RAID volume? I don't want to migrate or rebuild the 2 drives into a single 4 drive array, but instead have two RAID1 volumes--much like having 2 seperate TS-2xx NAS units each operating in RAID1.

This expansion option isn't listed in the Qnap manual. They only show migrating from a 2 drive RAID1 to a RAID5 larger array.

[pwilson]

Can the 4-bay units be initially configured with a single pair of RAID1 drives (2 bays still empty) and then later add a second RAID1 pair as a new RAID volume? I don't want to migrate or rebuild the 2 drives into a single 4 drive array, but instead have two RAID1 volumes--much like having 2 seperate TS-2xx NAS units each operating in RAID1.

Yes it is more than possible. Simply create a "new" RAID1 volume.

I personally think it is huge waste of space to do so on a 4-Bay NAS, but yes it is possible.

RAID1 (2 * 2TB Drives = 1.8 TB of space.
2 * (RAID1: 2 * 2TB Drives) = 2 * 1.8 TB of space. (3.6TB total space in two volumes).

RAID5 (4 * 2 TB Drives = 5.4TB of space.

[storageneeded]

Thanks for the quick answer. It is a waste of space, agreed. But, in this day of marginal hard drives, it's also more reliable than RAID5. Two drive failures will, at worst, wipe out half your data not all of it and you can duplicate critical data on both volumes making it very robust. And, yes, I know about RAID6, hot spares, etc. But they're not much more efficient than RAID1 in this case. You also avoid the painfully slow data migration process and (in my experience) 10+ hours of constant pounding on the drives.

Another big plus of RAID1 is the data is easily recoverable if the NAS itself fails. I also have a 2 bay QNAP I can use as a cold spare if the 4 bay unit fails to access at least one of the RAID1 pairs.

You may already be aware, but it's not that uncommon for 2 drives from the same production batch to fail in the same week in NAS use. There's a white paper published by Google and a University with some rather alarming statistics about that. Say a drive fails in your 4 drive RAID5 array, you pop in your handy spare (or worse order one and wait), and while the array is pounding itself to death rebuilding back to 4 drives another drive fails. Goodbye to ALL your NAS data and hope your have complete, current, and intact backups. For those who think that's far fetched, I've had it happen!

[P3R]

And, yes, I know about RAID6, hot spares, etc. But they're not much more efficient than RAID1 in this case.

With RAID 6 any two disks can fail and all data is still accessible. That's a very nice improvement in fault tolerance over your preferred configuration. RAID 10 offer the same redundancy as your configuration but with better performance.

All single disk volume configurations means less ongoing administrative work than multiple volume setups.

You also avoid the painfully slow data migration process...

That is correct. If 10 hours of migration is a too high prize for you to pay for better fault tolerance and easier administration then yes, you should go with dual RAID 1 volumes.

Also the RAID 1 volume needs to be synchronized but it is quicker and the volume is available for use through the complete process if that is important.

...10+ hours of constant pounding on the drives.

Well that is 10+ hours of doing exactly what disks are designed to do. If it was necessary to do that daily, then maybe I could start to accept it as being a risk for the longetivity of the disks.

I also have a 2 bay QNAP I can use as a cold spare if the 4 bay unit fails to access at least one of the RAID1 pairs.

It isn't supported but maybe you are correct and that it can work?

You may already be aware, but it's not that uncommon for 2 drives from the same production batch to fail in the same week in NAS use.

Yes that can happen.

If that is your fear, why not choose the configuration with the best possible fault tolerance?

There's a white paper published by Google and a University with some rather alarming statistics about that.

I can't remember seeing that, could you please supply a link to it?

Goodbye to ALL your NAS data and hope your have complete, current, and intact backups.

Regardless of RAID level used, RAID isn't and shouldn't be the protection for your data. It's always the backups that protects your data!

The reasons for using RAID is only to:
* Keep the data still easily accessible despite a reasonable number of disk failures
and/or
* Improve performance
and/or
* Offer easy expansion
and/or
* Offer larger volumes for ease of administration.

[storageneeded]

Thanks for the added comments. We all have our preferences. The double RAID1 gives me the option of storing less critical data on just one array and the critical data on both. 100% (all 4) of the drives would have to fail to lose the critical data stored redundantly. So, for that data, it's technically more reliable than any other 4 drive array. After having 2 drive failures in the same week destroy an entire RAID5 array, and having what's was left on the working drives be essentially useless, I'd rather keep it simple. You can mount any RAID1 drive on a PC and do a simple immediate copy of all the data in just a couple hours or less. You can't do that with RAID5, 6 or 10.

The Google paper is easy to find with, you guessed it, Google search. It got a lot of publicity when it came out in 2007 as Google was (and is) considered to be one of the largest users of hard drives in the world. Since then a couple of PhD university guys have taken Google's work and applied it to more typical drive usage.

[P3R]

The double RAID1 gives me the option of storing less critical data on just one array and the critical data on both. 100% (all 4) of the drives would have to fail to lose the critical data stored redundantly.

Yes data redundancy is the way to go to protect data.

In my opinion a smarter way to achieve that redundancy is to backup to at least two backup disks outside of the NAS. They will protect from many more threats than a double RAID 1 can. By always keeping at least one of those backups at another location, you can have very good data protection in a very affordable way.

You can mount any RAID1 drive on a PC and do a simple immediate copy of all the data in just a couple hours or less. You can't do that with RAID5, 6 or 10.

No but you can when using external disks as backup.

Anyway we definately do agree on: "We all have our preferences".

The Google paper is easy to find with, you guessed it, Google search. It got a lot of publicity when it came out in 2007 as Google was (and is) considered to be one of the largest users of hard drives in the world. Since then a couple of PhD university guys have taken Google's work and applied it to more typical drive usage.

Well I'm guessing you mean the Google paper titled Failure Trends in a Large Disk Drive Population. It contains a lot of interesting facts and I have linked to it in this forum several times. However since I don't find any support for "it's not that uncommon for 2 drives from the same production batch to fail in the same week in NAS use" in there, I guess the support must be in the work of "...a couple of PhD university guys...". Unfortunately the latter is the work I can't find despite searching for it. Please help enlighten the community with a link.