Best configuration for different sized disks

[figster983]

As I am getting to know N4F, I am looking for advice on the best configuration for these hard drives:

1 x 250GB
1 x 320GB
1 x 500GB
1 x 1TB

I am looking for as much space as possible, but require my data to survive at the least a single drive failure (as the terabyte drive is new, but the other three are ~2yrs old).

I would assume that there is some way to stripe the 250, 320 and 500gb drives together, then mirror the outcome with the terabyte drive, producing 1TB of total mirrored free space, but after looking through the settings, I am unable to see how I would go about doing that. Any help would be appreciated.

Thanks!

[ChriZathens]

You want to create a mirror of stripes...
But unfortunately you can only create a stripe of mirrors...
The way I see it, in order to have protection, with the disks you have now, you can create one mirror with the 250 & the 320GB disks and another one with the 500 & the 1 TB disks. Or a raidz with all drives
But total space will be limited to 750GB in both cases .. A lot of space wasted
But later you can change one by one with bigger ones. After changing all you will have the extended space

[ku-gew]

Or stripe the three small disks and, if possible, add the big one as mirror.

[figster983]

Ok, so I have been doing some more thinking. What if I was to add more drives to the mix in order to gain more space? I would most likely be using ZFS in a raidz, or raidz2 configuration. I understand (and am glad that) I can swap out smaller drives for larger drives under ZFS, as long as I don't try to add a drive. But a question I have is what if I want to shrink the pool of vdevs? Say I have 8 drives now, but later I only want to have 6. Is it possible to shrink it without recreating the pool while retaining my data intact?

Thanks for responding so quickly by the way!

[ChriZathens]

AFAIK removing a disk from a pool is not possible
But you can begin with a small number of drives eg 4
Later you can create a second vdev with another 4 and add it to the pool
This will add the space of the second vdev to the pool
Then you can change all disks in first vdev with bigger ones. Pool space will grow.
Later on, when in need for more space you can change all disks in second vdev with bigger ones.
Pool size will again grow and so on...
So essentially, growing your space is possible either by replacing disks with bigger ones, or adding another vdev, or do both
For example you can begin with 5x500GB hdds raidz(about 1.8TB usable space) and end up with 4 raidzs, each one with 5x4TB hdds ( usable space about 60TB) in one pool

[figster983]

Perfect. Hey, thanks for your help! I believe I'm getting a better hold on things now, and I should be good.

Thanks!

[olko]

Although I would personally not recommend this, but if you want to be really creative you can do the following to maximize space utilization and still have protection from single drive failure:

1) Partition you drives as following:
* ad1: ad1p1=250GB (250GB total)
* ad2: ad2p1=250GB, ad2p2=70GB (320GB total)
* ad3: ad3p1=250GB, ad3p2=70GB, ad3p3=180GB (500GB total)
* ad4: ad4p1=250GB, ad4p2=70GB, ad4p3=180GB, ad4p4=500GB (1000GB total)

2) Create your ZFS pool as following:
zpool create tank \
raidz ad1p1 ad2p1 ad3p1 ad4p1 \
raidz ad2p2 ad3p2 ad4p2 \
mirror ad3p3 ad4p3

This will give you 1070GB of protected space ((4-1)*250GB+(3-1)*70GB+(2/2)*180GB) and 500GB of unprotected leftover on ad4p4.

[fsbruva]

If you go the partitioned route, you will pay a pretty stiff performance penalty. Additionally, as you choose to upgrade your drives (failures, etc), you are chained to this same layout.

My recommendation would be to get another 1T, and put it into a mirror with the other 1T. Then, mirror the 250 to the 320, and leave the 500 online as a hot spare. If you truly don't trust your old drives, this will segregate the good from the bad, but still allow you to seamlessly recover from a drive failure. Also, it will keep your drive upgrade options open.