FreeNas for Home 2 x 4TB Disks Backup Solution?

[no_connection]

Remember, a mirror does not guarantee against data loss if one disk breaks as there is no redundancy left and if the remaining disk have an error it will be uncorrectable.
Yes there is not a huge chance that it will end up in broken files but it is still there. And as you will be reading the entire amount of data when you resilver to a replacement disk, stressing it, who knows what will happen.
A four drive Z2 seems a little wasteful but you still have parity while you resilver the replacement. Thus it tolerates one disk failure without data loss.
You can loose two disks without loosing the pool, but you have no guarantee against uncorrectable errors.

 

[danb35]

If you want to set up two disks in a mirror now, and at some time in the future change to a four-disk RAIDZ2, there are two ways I know of to make that happen.

The recommended/supported option is to back up your data, destroy the pool, create a new pool as the four-disk RAIDZ2, and restore your data.

The unsupported/"here be dragons" option is to create a degraded RAIDZ2 pool using sparse files to simulate two of the four disks, copy your data to it, and then replace the sparse files with (your original) real disks to give you redundancy. See http://forums.freenas.org/index.php...dz-3-of-4-drives-i-e-to-allow-migration.7748/ for a write-up on this procedure (he was simulating a single disk missing in a RAIDZ1, but the same process ought to work with two disks and a RAIDZ2). This would allow you to end up with the four-disk RAIDZ2 without using separate storage for backups, but there's a window of time while you're resilvering when you have no data redundancy. The wrong disk failure at that time could be catastrophic.

Performance is a factor here as well. As I understand it, a four-disk pool consisting of two mirrored pairs will have better performance than a four-disk RAIDZ2 pool.

 

[SpiritFly]

Okay so let's say you're in my shoes now. You have the 2 x 4TBs at hand and a hp proliant ML310e Gen8 v2 server that will be arriving tomorrow. Your only need for backup would be family photos, videos and work files/documents. All in all it shouldn't exceed 4TB anytime soon, at least not in the following 5 years to come. How would you setup the 2 x 4TBs and would you get anything more or exclude something from the equation?

Btw I'm considering creating a separate pool of 1TB without redundancy for storing Divx movies, music and files that can be easily downloaded again from the net to keep my 4TBs only for my important data.

 

[danb35]

If you have 2x 4 TB drives, and don't expect or want to get more shortly, I'd set up the drives as a mirror and be happy. Heck, I'm using RAIDZ1 for my pool, which is more susceptible to loss from disk failure. I'd like to set it up as RAIDZ2, but that's just going to have to wait for a while. In the meantime, I run regular SMART tests and scrubs (which you should as well, and make sure your server can email notifications to you).

 

[gpsguy]

In addition to what danb35 said, I'd suggest you keep a separate backup or three of any irreplaceable files - like the family photo's.

Other than that, you should be good to go.


Sent from my phone

 

[AleQQ]

Or you could set them up in a RAIDZ2 pool, which would give you the same capacity (~ 8 TB), but different redundancy--RAIDZ2 would tolerate the failure of any two disks without data loss, compared to only one in each mirror with mirrored pairs.

Is there really a benefit in this case to doing "Raid 10" on ZFS vs RaidZ2? Or do benefits change as your quantity of drives scales up? I know Raid Z3 is an option. Also, is there any benefit (other than rw speeds) of adding the 2 additional drives as a second vdev in the same pool vs simply adding another pool?

 

[danb35]

"RAID 10," as I understand it, will have better performance than RAIDZ. A four-disk RAIDZ2 vdev will have better redundancy than a four-disk "RAID 10", because any two drives can fail without data loss. As the vdev scales up, you'll have better capacity with RAIDZ2--for example, with a six-disk RAIDZ2, you'll be losing 1/3 of your total capacity to redundancy, while with three mirrored pairs, you'll lose half.

Adding vdevs to the same pool simplifies administration--all your storage is in a single place, and you can dynamically carve it up however you need. You won't run into a situation where one pool is full while the other has space free. It does, however, carry some risk (see my "hating your data" scenario).

 

[AleQQ]

Makes sense. Thanks! I'm off to find a good book on ZFS. I think cyberjock or someone linked one somewhere....