I'm considering making a NAS with freenas, Got a few questions:
This is my plan, to create a series of Virtual Devices each with 3 drives in RaidZ1 (I know RaidZ2 is better, but for now ignore this). This would give me expandability as I can add a set of 3 drives as a new Vdev and expand the Zpool. However as the Zpool grows, this provides no more redundancy than the 1 disk of redundancy per Vdev; So even if I have say 3 sets of Vdevs and therefore 3 drives of parity, i am still limited to one drive of parity in some cases before the whole Zpool fails.
Is there no way to create multiple zpools each consisting of only one Vdev (eg 3 drives in RaidZ1) and then make them appear as a single [virtual] drive. This would give the benefit of if a single Vdev fails (eg more than one drive fails) Only the data in THAT Vdev is lost, NOT the whole Zpool.
I guess what I am asking is if I can create a SPAN of Zpools either from freenas or in windows, so that I can have multiple Zpools, which appear to me as a single drive, but each zpool is redundant, but If I did lose one Vdev, only the data in that Zpool would be lost.
Heres a link with me trying to illustrate what I'm talking about, and show expandability.
http://i.imgur.com/K2a6u.png
It seems to me that the redundancy in ZFS is only based on low numbers of Vdevs with high number of drives in them; You lose relative safety if you have higher numbers of vdevs with low number of drives in a zpool. Eg, even with mirroring (the best form of redundancy in a Vdev) if you had a zpool of 5 vdevs each with 2 drives mirrored (total 10 drives) you still only have a possible redundancy of 2 drives before the whole Zpool can fail!
I realise that i could use RaidZ2, but if I wanted to keep the initial size of the Vdevs down, but expand later, this would mean say 4 drives per Vdev in RaidZ2, expand up to 3 Vdevs (12 disks) and with 6! disks of parity, I still only get a possible 2 disks of redundancy, Even if I was to mirror I have the same problem, (eg a vdev of 2 disks in mirror)
What I want is to keep the size of the Vdisks down, so that I dont have to buy say 5 x 3/4 TBers upfront, but still have a high redundancy while appearing as a single disk to me.
This is my plan, to create a series of Virtual Devices each with 3 drives in RaidZ1 (I know RaidZ2 is better, but for now ignore this). This would give me expandability as I can add a set of 3 drives as a new Vdev and expand the Zpool. However as the Zpool grows, this provides no more redundancy than the 1 disk of redundancy per Vdev; So even if I have say 3 sets of Vdevs and therefore 3 drives of parity, i am still limited to one drive of parity in some cases before the whole Zpool fails.
Is there no way to create multiple zpools each consisting of only one Vdev (eg 3 drives in RaidZ1) and then make them appear as a single [virtual] drive. This would give the benefit of if a single Vdev fails (eg more than one drive fails) Only the data in THAT Vdev is lost, NOT the whole Zpool.
I guess what I am asking is if I can create a SPAN of Zpools either from freenas or in windows, so that I can have multiple Zpools, which appear to me as a single drive, but each zpool is redundant, but If I did lose one Vdev, only the data in that Zpool would be lost.
Heres a link with me trying to illustrate what I'm talking about, and show expandability.
http://i.imgur.com/K2a6u.png
It seems to me that the redundancy in ZFS is only based on low numbers of Vdevs with high number of drives in them; You lose relative safety if you have higher numbers of vdevs with low number of drives in a zpool. Eg, even with mirroring (the best form of redundancy in a Vdev) if you had a zpool of 5 vdevs each with 2 drives mirrored (total 10 drives) you still only have a possible redundancy of 2 drives before the whole Zpool can fail!
I realise that i could use RaidZ2, but if I wanted to keep the initial size of the Vdevs down, but expand later, this would mean say 4 drives per Vdev in RaidZ2, expand up to 3 Vdevs (12 disks) and with 6! disks of parity, I still only get a possible 2 disks of redundancy, Even if I was to mirror I have the same problem, (eg a vdev of 2 disks in mirror)
What I want is to keep the size of the Vdisks down, so that I dont have to buy say 5 x 3/4 TBers upfront, but still have a high redundancy while appearing as a single disk to me.