newbie new installation, pool suggestion for 4 drives (which then will be 8)

[horizonbrave]

Hi,
by posting in the noob section I hope I'll be forgiven (of course I haven't done my homework!).
I'm starting to use freenas with 4 drives of the same size (4TB, that's what I can afford now).
The Dell T320 has 8 bays, so I'm going to buy another 4 in another time.
To keep things easy I'll start with just one pool using the 4 drives.
I have backups.

Which setup would you please suggest (that I could easily extend later to the additional 4 drives of the same size)?
For my usage 3 drives tolerance (on a 8 drives system) is enough but I'll consider 4 in case if it's easier.
Thanks a lot

 

[horizonbrave]

Idea: what about considering my nas as 6-7 bay unit?
I could use the remaning bay(s) for a separate Vdev for backup (of the same capacity of the other 6-7 drives Z3 Vdev - let's say I'll use 2TB drives).
I'm aware that wouldn't be a real backup as it should be located on another machine.
Or can I even consider striping the whole 6-7 drives Vdev to a single drive of the same capacity?
I know you're going to send me to do my homework... :)

EDIT: I can eventually afford 8x 2TB drives to fully populate the unit in case

 

[garm]

If you intend to use the same machine for burn in of new drives and such I would leave atleast 1 bay empty. I would recommend getting two more drives and set up a 6 wide RAIDZ2 pool, your upgrade path would then be to replace each of the 6 drives with bigger once using the two empty slots.

 

[diedrichg]

Agreed. You really want a (6) drive RAIDZ2 pool, anything less will just be wasting space. You can build it with your (4) 4TB drives and (2) other drives you have laying around - keep in mind that until those two smaller drives are replaced with 4 TB or larger drives they will be registered as the same size as the smallest drives. But, when you get the cash for two more 4TB drives and replace the smaller drives (one at a time), your pool will then grow to the size you originally intended of (6) 4TB.

Example:
(4) 4TB
(2) 1TB
Will be built as (6) 1TB drives pool.
= 2.86 TiB usable space

Replace the 1TB drives with 4TB drives:
(6) 4TB
= 11.46 TiB usable space

 

[horizonbrave]

6-10 (drives) RAIDZ1 x 2

the above quote is from this 2014 article.
Please what do you think about that? Thanks :)

 

[sretalla]

6-10 (drives) RAIDZ1 x 2
what do you think about that?

How much of a gambler are you... RAIDZ1 allows a single drive failure per VDEV... if you have 2 of them in a pool, you have the possibility that 2 drives fail (1 in each VDEV) and you're good, but if the 2 failing drives are the same VDEV, your data is all gone, both VDEVs, the whole pool... worth the gamble?

 

[danb35]

None of us can tell you what you should do, but there are a few things you may want to consider:

• More vdevs -> more IOPS -> better random r/w performance
• Mirrored vdevs resilver faster than RAIDZn vdevs
• Pools with striped mirrors are simpler to expand--just add another pair of disks when you need more space. That will also improve performance.
• Pools with striped mirrors are also easier to expand by replacing disks--you only have to replace two disks to see an increase.
• Mirrored pools sacrifice at least half your total capacity to redundancy
• Mirrored pools have only one disk's worth of guaranteed redundancy. In a six-disk pool of striped mirrors, for example, up to three disks could fail without data loss, if those were one disk out of each vdev. However, if both disks in one vdev fail, all data on the pool is lost.

 

[horizonbrave]

Mirrored pools have only one disk's worth of guaranteed redundancy. In a six-disk pool of striped mirrors, for example, up to three disks could fail without data loss, if those were one disk out of each vdev. However, if both disks in one vdev fail, all data on the pool is lost.

Thanks. But I could eventually also create pools of mirrored vdev, where each vdev is a raidz2, right?
I'm aware that I'll be loosing half of the raw capacity though.
I guess I could do that with 8 drives but what about if I start now creating a pool with one single raidz2 vdev made of 4 drives: could I later add another similar vdev to the pool and configure it like its mirror? I'm pretty sure the only advantage would be performance.. I can't figure it out if it's adding even more redundancy. I know I should keep reading.. thanks for helping!

 

[garm]

No, vdevs are striped together in a pool. Redundancy happens in each vdev