Increasing ZFS pool

[foxdoismil]

1) First the tragedy:
I have two (supposed to be redundant) nas4free boxes.
One has 5 disks RaidZ2 and the other 6 disks RaidZ2 (Seagate st4000vn000 4TB NAS hard disks)

Some time ago, the 6 disk system had 2 dead drives at once! In the first moment I thought it was the LSI SAS 9211-8i controller, but after some testing I concluded that the Seagate drives were dead beyond any doubt. I stopped this NAS operation waiting for new controller and drives to arrive.

Less than 2 weeks later, before I could buy the new drives, the other system had a main drive crash and the NAS stopped booting.
So, I had data in 11 disks RaidZ2 and in 2 weeks I was completely off-line.

Of course, after some time I replaced and resilvered the 2 dead drives with new ones, and also the main drive of the second NAS, both are up and running again.

2) Now the doubts that are hurting my heart:
Of course I will increase both systems to RaidZ3 (or more if that exists) and the hard disks are still going to be the Seagate (although I do not trust them so much any more). What size ZFS RaidZ3 would you create? 6, 7 or 8 Disks? (I do not have bays for more)

Thanks for the help

[kenZ71]

Using a raidz2 and SMART disk monitoring it hard to lose data. Make that raidz3 and your even more protected. However Fire, theft, flood or even user error makes off site cold backup critical.

[Parkcomm]

Two disks at he same time will go from time to time - especially if you buy them and install them in batches.

You should boot from a USB and have a spare drive handy in case of failure - thats an easy solve costing $2

Personally I wouldn't bother with raidz3