ZFS on hardware RAID

[bob]

hi,

I am setting up a NAS box with the following hardware.

Atom D525 Mobo
Adaptec 3805 4x PCIe card
4x 2 Tb SATA drives
System on CF card (With CF to SATA adapter)
4 Gb RAM

I am considering using 64 bit Freenas 8. I am now considering the file system to use and I am not keen on using UFS (Have spent to much time already in my life on endless fschk on UFS and old Ext systems) so the I am left with ZFS. My question is now what is the best strategy to use for the underlying RAID array. Should I just put the controller in JBOD mode and use RAIDz for redundancy? Or should I use RAID 10 on the controller and just format this as ZFS in Freenas? Or RAID 5 on the controller and RAIDz as file system? There are many options but I don't like the idea of "RAID on RAID", have bad experiences with this from before in other OS.

I am not so concerned with speed (will be enough for what I need any how) or space (I can live with having 3.6 Tb of space which is what I get from a RAID 10 array). my main concerns is stability (both filesystem and the OS itself) and some redundancy. With a Linux box I would have used RAID10 and Ext3, that would be a good setup for me, but I am lost with with ZFS here.

Thank you

/Bob

 

[matthewowen01]

the best strategy for an underlying RAID is to not use it.

let ZFS do it. place the drives in either a raidz (think raid5), raidz2(think raid6) , or a pair of mirrors (think raid10)

 

[bob]

Thanks for the reply, that was kind of what I was thinking. I will still use the RAID card i think, as I don't have enough SATA connections on the motherboard, and since I already have the card since before. I guess putting the RAID card in JBOD mode should do it?

Thanks

/Bob

 

[Jesster009]

the best strategy for an underlying RAID is to not use it.

let ZFS do it. place the drives in either a raidz (think raid5), raidz2(think raid6) , or a pair of mirrors (think raid10)

I'm curious as to why you would choose to use ZFS's raid rather then the dedicated card?

Also i'm not sure if this is still the case but when you use ZFS's raid features you can not just add disks at a later time expanding the array as you should be able to with the hardware card.

Thanks
Jesse

 

[Milhouse]

I'm curious as to why you would choose to use ZFS's raid rather then the dedicated card?

The often quoted answer is how do you access your data when the dedicated card fails (and may no longer be available to buy, except maybe via ebay?) With software RAID (ie. ZFS) you can connect the disks to another machine and access your data, no special controller required.

Also i'm not sure if this is still the case but when you use ZFS's raid features you can not just add disks at a later time expanding the array as you should be able to with the hardware card.

Should, but often can't. With ZFS, you can expand the size of the array by replacing all the disks with larger equivalents and allow ZFS to expand into the newly available space, or you can add additional vdevs to the zpool creating a striped array.

 

[matthewowen01]

expanding is difficult but doable.

you must keep the underlying vdevs. if you start with a raidz2, you must have that same raidz2 at the end. however, you can add additional vdevs to the pool. you can attach an additional raidz2 to the pool easily.

you can also grow the disks of a vdev, say you had a raidz2 pool of 6, 1 TB disks, you could slowly swap out each disk with a 2 TB disk, let the pool resilver each time and once all the disks were swapped, you'd have you extra space (you may have to set an auto expand flag on the pool) it's slow but possible.

 

[Joshua Parker Ruehlig]

Hey may I also recommend a different mobo, this will save you money by letting you buy desktop ram. Also it will allow you to get 8GB ram instead of the 4GB (which is bare minimum for zfs).

http://www.amazon.com/gp/product/B004LDEQHA/?tag=ozlp-20