raidz2 options

[DataKeeper]

Currently have 18 new and tested 4TB WD RED drives in a 24-bay chassis allowing an additional 6 drives later. I have 2 primary storage uses for this system.. 1. Personal Photos and Documents (PPDs) & 2. Media mostly with other shared storage. The PPDs are very important to me and thus the originals are stored on my desktop and another external drive kept in a fire/water proof safe. The PPDs on this freenas server would be mostly for backup and rarely accessed. The Media will be accessed 24/7 in 1 way or another via music streaming to various rooms of the house to PLEX, etc.

With 18 drives currently I could create a Media pool with a 6 drive vdev raidz2 then extend this with a second 6 drive vdev raidz2. I can extend this later with an additional 6 drive vdev. Next.. Create a new pool, say PPDs, with a 5 drive vdev raidz2. This leaves 1 spare drive available as a hot spare if needed down the road.

Second option with separate pools would be 2 vdevs of 8 drives, a single vdev with 6 drives and 2 hot spares.

Third option with separate pools would be 2 vdevs of 8 drives, a single vdev raidz3 with 7 drives and 1 hot spare.

My questions are..

1. Does it make sense to create 2 different pools (say ppds & media) or a single pool with datasets to separate them?
2. Is replication easier or better from its own pool or a dataset?
   
3. Am I correct in believing that by extending the Media pool it becomes a mirrored raidz2 automatically?
   
4. My understanding is that a hot spare, or two, are now supported and allow for safer reslivering when a drive is just failing as it may not completely degraded. Are they now worth having?

For the most part the Media can easily be replaced and I'm not super concerned over that data. My photo collection is worth substantially more to me and I'm just looking for the best storage option.

Comments are more then welcomed!
Thanks

 

[anodos]

My questions are..

1. Does it make sense to create 2 different pools (say ppds & media) or a single pool with datasets to separate them?
2. Is replication easier or better from its own pool or a dataset?
   
3. Am I correct in believing that by extending the Media pool it becomes a mirrored raidz2 automatically?
   
4. My understanding is that a hot spare, or two, are now supported and allow for safer reslivering when a drive is just failing as it may not completely degraded. Are they now worth having?

My answers:
1) I personally prefer to make a single large zpool. I've had multiple zpools on servers, and I always end up not being able to use space as efficiently as times when I did one big zpool.
2) Define easier. Typically you would replicate to a second FreeNAS server. The bottleneck will always be your network.
3) Not sure what you mean by this. You can have different types of vdevs (2/3-way mirrors, Z1,-3, single disk), but vdevs are always striped.
4) If you're using 6-disk raidz2 vdevs, I don't see much point in having a hot-spare. With a 24-bay chassis, I'd consider 4*6-disk Raidz2 vdevs or 3*8-disk Raidz2 vdevs. If you need lots of IOPS, then switch to mirrors.

Additional thoughts:
Label your drive bays / keep track of which disks are in which bay. It sucks to pull the wrong disk.
Make sure you have a good backup strategy.

 

[Bidule0hm]

1) The third option seems to be the best for reliability (assuming the RAID-Z3 is for your PPDs) but the problem is space usage as anodos pointed.

2) I agree with anodos.

3) Idem.

4) I consider hot spares useless (excepted for enterprise when you don't want downtime or if you can't physically replace a drive within a few days) because the drive is wearing itself doing nothing for most (if not all) of his life. I'd keep it as a cold spare ;) also, if you want a hot spare on a RAID-Z2 it's better to use it directly in the "RAID-Z2" to form a RAID-Z3 (same cost, same power usage, same everything, excepted better reliability :)).

 

[Robert Trevellyan]

I agree with both above that 1 pool is better for ease of management and space utilization. However, for completeness I think it's worth reminding you that if you lose a vdev you lose the pool. With RAIDZ2 vdevs this would be unlikely, but stuff happens...

 

[DataKeeper]

Ok so I'm going to go with a single pool for now. I created a pool called 'garage' with a 6-drive vdev then 1 more 6-drive vdev extended to the first. I have another 6 drives however 1 is a replacement so going through tests now. Once completed I'll extend those to the first giving about 42TB of usable space with 6 free bays for later expansion.

I have about 8TB of data to move over, maybe 3 more shortly afterwards so tons of space left. :D