SOLVED A quick question to clarify my understanding of which RaidZ option to use

[Hazimil]

Hi All, just a quick question to clarify my understanding of which RaidZ option to use. I have read the manual, resources section and ZFS primer, but just wanted to be sure that I have read and understood it correctly.

I plan to build a new box with 8* 8TB WD Red, giving a total of 64TB usable data in one vdev:

1. If i use RaidZ, this means I will get a total usage capacity of 56TB with the fault tolerance of 1 drive failure before I lose all data.
2. If i use RaidZ2, this means I will get a total usage capacity of 48TB with the fault tolerance of 2 drive failures before I lose all data.
3. If i use RaidZ3, this means I will get a total usage capacity of 40TB with the fault tolerance of 3 drive failures before I lose all data.

Am I right in understanding, that by drive failure, it means any of the 8 drives i.e. not a specific drive? Also, that the NAS will function with the failed (or removed drives) but be at risk until I replace it/them?

If I've understood this right, I be going for either RaidZ2 or RaidZ3 (not made my mind up yet.

Thanks.
Jonathan

 

[Jailer]

Am I right in understanding, that by drive failure, it means any of the 8 drives i.e. not a specific drive?

Correct.

Also, that the NAS will function with the failed (or removed drives) but be at risk until I replace it/them?

Correct. Your pool will operate in a degraded state but will otherwise be functional. It's advised to replace the drive ASAP as you've lost some of your redundancy until you do.

You might want to take a look at @Bidule0hm RAID capacity calculator for a closer estimation of usable space. Also you don't want to fill your pool past 80% or performance tanks so work that into your usable space as well.

 

[rs225]

If your goal is not to lose all your data, all you need to do is make a backup.

 

[Hazimil]

@Jailer , Thanks for the reply. I forgot about the 80% rule!
@rs225 , Yep, I plan to backup the important data from the NAS, just wanted to ensure my understanding of RaidZ was right.

Cheers.

 

[Stux]

Hi All, just a quick question to clarify my understanding of which RaidZ option to use. I have read the manual, resources section and ZFS primer, but just wanted to be sure that I have read and understood it correctly.

I plan to build a new box with 8* 8TB WD Red, giving a total of 64TB usable data in one vdev:

1. If i use RaidZ, this means I will get a total usage capacity of 56TB with the fault tolerance of 1 drive failure before I lose all data.
2. If i use RaidZ2, this means I will get a total usage capacity of 48TB with the fault tolerance of 2 drive failures before I lose all data.
3. If i use RaidZ3, this means I will get a total usage capacity of 40TB with the fault tolerance of 3 drive failures before I lose all data.

Am I right in understanding, that by drive failure, it means any of the 8 drives i.e. not a specific drive? Also, that the NAS will function with the failed (or removed drives) but be at risk until I replace it/them?

If I've understood this right, I be going for either RaidZ2 or RaidZ3 (not made my mind up yet.

Thanks.
Jonathan

Its a simplistic explanation, but is roughly correct.

The key is that with RaidZ (or RAID5), once you lose one drive, you have no redundancy, and even a single corrupt block in the pool will result in lost data, but not necessarily a total loss.

And drives fail. They really do, so you will suffer a drive failure eventually.

With RaidZ2, once you lose a drive, a single corrupt block, or in fact many thousands, will probably not result in lost data, unless the corrupt block on a given disk, is co-located with another corrupt block on one of the other disks. A second drive loss at this stage, is just a large amount of corrupt blocks ;)

RaidZ3 takes this to the next level. And now you can withstand co-located corrupt blocks as well as a drive failure, or 2 or 3 total drive failures.

I would go with RaidZ2. And a backup. For a total of 6x8TB of storage, which you should plan to upgrade/extend once you get to 80% usage, and before you get to 90% usage. Ie, by adding another 8 drives, which may involve a bigger chassis, but you can cross that bridge when you get there.

Also, TB is not TiB, and that may surprise you. You storage in TiB will be about 9.something% less.