Storage expansion strategy

[weingeist]

Hi all

I have been running my small home server for the last two years and everything works perfectly so far (specs can be found in my signature). I use it for storage of my personal data (about 10%) as well as movies and series (about 90%). I have a backup of my personal data on a 4TB external WD red attached to a Raspberry Pi.

My motherboard has 6 Sata connectors, and my case has 6 bays. At the moment, there is only one single mirror of 2x8TB, which is now quite full (82%) and I'm trying to think of the best expansion strategy to get to my long term goal: a 6-disk Raid Z2. I purchased 4 more 8TB disks but I'm not sure on how to proceed. The way I see it there are the following possibilities:

• Expand by striping another 2x8TB mirror, and when the time comes a third one. Pro: easy, uncomplicated, save. Con: only 50% storage efficiency, no Raid Z2.
• Create new zpool with a 4 disk Raid Z2, migrate data to new pool. Destroy the mirror. When the time comes (say another two years), expanding zpool to 6 disks, hoping this feature eventually is finished and makes it to Freenas. However, according to this Reddit thread, the existing parity data is not rewritten, but only redistributed. This would result in an uncertain storage efficiency of somewhere between 50% and 66%. Anybody has more info on this?
• Not my favorite: buy another disk, remove mirror, fill up NAS with 5 new disks and one from the mirror and directly create fresh 6-disk Raid Z2, attach 2nd mirror disk over USB for migrating the data.
  I'm no fan of this method, since at one point, all data is only stored on a single disk. As explained before, my important personal data is backuped, the movies and series are not, since they are replaceable, although it would be incredibly tedious to restore it. Another disadvantage of this in my eyes is the massive increase in storage, which is somewhat unnecessary at this point. It will take my probably 3-5 years to fill up the next 8tb, having 16tb free for this time seems like a waste of operating hours of the disks.
• Quite experimental and no idea if possible, yet alone save: Stripe a second 2x8TB mirror to my existing one. When it is full, remove one disk from each vdev, leaving it in a degraded state. Then, I have 4 spare disks and more importantly, 4 free Sata ports, which I use to create a degraded 6-disk Raid Z2 with help of two virtual dummy disks. No idea if something like this exists? This is somewhat my preferred procedure, since it allows me for a two-step expansion and I would end up with a fresh 6-disk Raid Z2.

Does anybody know of a possibility I am failing to see? Or does anybody have some insight on the last procedure, is it feasible and not terribly unsafe?

Remember:
- I'm limited to 6 sata ports
- I don't have tons of spare disks, therefore it is difficult to clean out my NAS for building pools from scratch.
- It is a home NAS, therefore some small risk of losing my movies and series is acceptable. If a disk dies in the wrong moment, well tough luck.

I appreciate any help,
cheers,
weingeist

 

[myoung]

Expand by striping another 2x8TB mirror, and when the time comes a third one. Pro: easy, uncomplicated, save. Con: only 50% storage efficiency, no Raid Z2.

This is probably your best option.

Not my favorite: buy another disk, remove mirror, fill up NAS with 5 new disks and one from the mirror and directly create fresh 6-disk Raid Z2, attach 2nd mirror disk over USB for migrating the data.
I'm no fan of this method, since at one point, all data is only stored on a single disk. As explained before, my important personal data is backuped, the movies and series are not, since they are replaceable, although it would be incredibly tedious to restore it. Another disadvantage of this in my eyes is the massive increase in storage, which is somewhat unnecessary at this point. It will take my probably 3-5 years to fill up the next 8tb, having 16tb free for this time seems like a waste of operating hours of the disks.

This option isn't too bad. In addition, you could backup your data to the cloud. After your rebuild your pool, and transfer data from your single disk, scrub and restore anything that is corrupt from the cloud. Check your options, but generally it is free to put stuff on the cloud and you pay to pull it back. So, if your don't have to restore much and you delete it after you verify you don't have corruption, you shouldn't have to pay huge cloud fees.

Your other two ideas are not good ideas.

Getting an HBA would make it a lot easier to juggle drives because you aren't limited to 6 SATA ports.

 

[Arubial1229]

I would backup everything to an external drive and then rebuild the pool with 6 drives using RAIDz2, but that's me. When using ZFS for large media storage, give me RAIDz2 over mirrors any day.