Hi,
I’m a new user for TrueNAS. My question is related to raidz(1) vs raidz2. I’m using this machine purely for personal backup and am (currently) not looking to do anything ‘more advanced’ with it. Speeds/Peformance is not a priority. Stability and security is.
I recently purchased 3 new hard drives to have in a raidz1 config which I was advised by a friend. However, browsing for around for another issue (that is resolved) I stumbled on suggestions that raidz2 would be a better option. There is however a lot of information and opinions out there that is a bit overwhelming to sift through as a new guy.
So I hope to get a clearer answer if I really ought to invest in another disk for a raidz2 config (I dont have budget for more) or if what I have is sufficient for my purposes.
Thanks in advance and if you need more info to answer my question, just let me know!
Simply put, either can cope with sector errors, but in case of a complete drive failure, raidz1 is vulnerable to any further issue, which would result in file loss (sector error) or complete pool loss (drive failure), while raidz2 would still cope. Resilver can take days with large HDDs, and is stressful on the drives.
You cannot convert from raidz1 to raidz2 later.
In either case, backups are highly recommended.
If you dont need the space, you could also go 3-way mirror with the drives you have. This will give you faster resilver times (no parity) and the same level of resilience as a raidz2 . Also ~ 3x read speed.
Mirrors are more flexible (can change width, add or remove vdevs), but 3-way mirrors (for good resiliency) are not as space-efficient as raidz2 (33% vs. 50% minimum, 67-75% for “sweet spot” 6- to 8-wide raidz2) and thus a lot more expensive. You get what you pay for. https://louwrentius.com/the-hidden-cost-of-using-zfs-for-your-home-nas.html
The drives are 6TB each. The main clunk of it is just for data storage that is not vital (though always a pain if data gets lost).
For the more important data, I already have additional backup options in place.
Yes, I realized that raidz2 requires a minimum of 4 drives (more is out of budget at this time). That is why I asked if, considering my situation, I really need to go for that and buy a 4th disk or if raidz1 may be sufficient.
From what has been said so far, it sounds like raidz2 is the way to go.
I would reccomend going with a two-way mirror using two 14TB drives then, but if you aleeady have the drives 5 (or better, 6) of them in RAIDZ2 is truly the realistically (since you need space) safest option you have.
You will probably fine with 3 of them in RAIDZ, though it will scale awfully.
I already have 3x 6TB drives. Currently my options are use the 3 drives in raidz1 or adding a 4th for raidz2. I cannot go beyond that point at this time, though maybe in the future.
First, check that these drives are not SMR. Which model?
If the drives are CMR, I’d advise for a fourth drive and raidz2. Future expansion could be by adding a further vdev, by replacing drives with larger ones, and/or through raidz expansion when it eventually lands in a release version. But raidz expansion is all about widening vdevs, not about increasing raidz level, so better start with raidz2, as widening raidz1 would only make it less and less secure.
Ideally, I would agree. But realistically, if money is a concern, starting with a 4-wide raidz2 and expanding up to 6-8 drives looks to be a better plan than starting with 3-wide raidz1 and either enlarging raidz1 or adding further 3-wide vdevs.
The one and only compromise I see is that raidz expansion does not reflow existing data. Beside backup-destroy-restore, a solution would be to run in-place rebalancing, which requires enough free space, so doing the expansion soon enough for the expanded pool to be less than 50% full.
