Different sized disks - help me watch out for my data

[Trio]

Hi.
I've just installed FreeNAS on a dedicated computer of mine.

Specs:
ASRock E350M1
8GB DDR3 1066 RAM
1xSamsung 2TB disk
1xWestern Digital 2TB disk
1xWestern Digital 3TB disk
Kingston 4GB USB pendrive for FreeNAS

I'm thinking about buying a Western Digital Red 3TB disk, but it hasn't been done yet.

What I would like to do is setting some sort of RAID backup (RAID5?) for my usage, so that in case of a disk breaks I don't use any data.
I'm using ZFS.

My wish: I was thinking of making a storage pool and add all drives to the pool. In case of a bad disk I could simply "unmount" it, and the system would copy all contents to the pool leaving the bad drive ready for removal, next thing is to add the disk to the pool and carry on using the NAS. Possible? What happens to the pool if a disk suddently dies?

Could you please tell me what are my options? I know differenct sized/types of disks isn't optimal, but I can't afford to buy four new disks - eg. WD Red.

Thanks in advance,
Michael

 

[fracai]

There are a few things here.

1) If you combine disks of different sizes, you'll be limited by the size of the smallest. So putting two 2TB drives together with two 3TB drives is like using four 2TB drives (RAIDZ1 would yield around 6TB). ZFS will work just fine with that and you can always replace the 2TB drives at a later date, which will expand your size to use all as 3TB (9TB).

2) You generally don't need to worry about "unmounting" drives and telling the system to copy the contents when a drive dies. Basically, if you have four drives in a RAIDZ1 and one drive dies, you'll offline the bad drive (if necessary), insert a new drive, and tell the system to replace the old with the new. The replacement triggers a "resilver", which uses the information on the still good drives to fill the new drive. When it's done, your system will be protected again. Resilvering will impact the responsiveness of the system, but you can continue to use it as normal.

3) Keep in mind that if you build your system with three drives, you can't add a fourth to the pool without damaging your redundancy. If you were to do so, you'd have three drives with one drive redundancy and one drive with no redundancy. If that new drive dies you'd lose all your data. In other words, plan ahead. If you're going to want to have a four drive system, wait to build it until you can get that fourth drive. You can also expand your pool by adding a multiple drives as a new RAIDZ1, or even a new pool. Those would of course require adding multiple drives at a time though.