Currently running a 2 disk mirrored system with 8TB drives. Thinking about expanding and considering 4 more 8TB drives. I know I have to rebuild the pool either way and the resultant available space is the same either way. So is there any benefit to one method over the other?
Mostly used for media storage.
You can expand without rebuilding by simply adding two more mirror vdevs.
If you go for raidz (and more space), 6-wide raidz2 is better as it is more resilient: It can lose any two drives, as opposed to “one drive in each vdev” with either 2-way mirrors or raidz1 (i.e. lose two in the same vdev, loose all). Raidz1 is generally advised against with large drives.
Thank you for the input. I knew raidz1 is not recommended for large drives, I guess I am just not clear on where the breakpoint is as far as drive size.
Mirrored probably is not recommended for the same reason, right? (mirrored would certainly be easier and I could add 2 now and 2 later, I was just thinking that if I can afford 4 drives now, added resiliency would be good.
“RAID5 is dead” began floating around when drives went above 1 TB, and the same reasoning applies to raidz1. And indeed to 2-way mirrors, taking account of the total size of the vdev/array, so your 8 TB drives are indeed large enough to be of concern, dependig on how paranoid you are.
If you can afford to migrate to a raidz2, go for it.
Suggested reading: Assessing the Potential for Data Loss | TrueNAS Community.
Theoretically, with Electric Eel, you can create a 4-way RaidZ2 pool, migrate to that, and then add your other two disks to the raidz2.
More precisely: Add a first drive, let it extend and scrub afterwards; then add the second drive, and let the second scrub finish. Do not attempt to cut corners or to add two drives at the same time, the result appears to be “undefined”.
Then run the rebalancing script to rewrite the data with the new stripe width.
I am really curious how well this ends up working, the pitfalls, and what not. I will of course test it out once EE becomes an RC1 release.
EE is RC.2 now
(Blah blah blah blah)
Laugh Out Loud (LOL), damn, you got me and made me laugh. My daughter said “What, a little computer joke?”
Guess when I get back home from visiting the daughter, I will need to test drive that. I really didn’t realize it was RC2
Thanks for making me laugh!
So keep the mirror, set up the 4 drive raidz2 pool, move the data over then expand the pool to 5 drives (and then 6) using the two existing drives? I thought I had read expanding a pool by adding drives was not feasible…if it is, that sounds like a great way to do it. Would I be able to rename the new pool to the old pool name and keep the shares and permissions from the old pool (permissions seem to be the bane of my existence, hopefully my understanding of how they work improves once I wipe my laptop and put linux on it to play around with)
(I have time to plan (and research), I need to swap into a better case…possibly repurposing a fractal define R6 from work and buy the drives, none of which will happen in the next month since I am moving over the next 2-1/2 weeks and have plenty of house related tasks to deal with…including putting up a fence for my dog).
It is not currently, but will be in SCALE 24.10 (Electric Eel). It’s currently in beta and will be released in about 2 weeks (hopefully). RAIDZ expansion is a new feature
