ZFS ZFS RAID10 or RSYNC?

Aknot

Aknot

Are there any advantages to set up a mirror between two mirrored pair of ZFS disks [RAID10] than using RSYNC between two separate pairs of mirrored disks?

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In the rsync situation the second disk would not take over for the first one automatically when the first one breaks.

rsync can be pretty intense from a disk traffic standpoint.
 
So two mirror pairs, mirrored? Not trying to get any extra space out of the four disks? You could lose 3 of the 4 drives and still have the data. But there may be better configurations for the 4 drives for data integrity.

Aknot said:
Ease of replacing disks in case of failure, as I don't have any spares, with the exact same specs.
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That is why setting up partitions is useful.
Partitions can be used for pretty much any kind of ZFS construct, so you can get any disk that's bigger and use it.
If I recall correctly a vdev will use the smallest size physical device so if you create a mirror with a 2T and a 4T drive even using whole device, you have a mirror of size 2T
 
I think you are saying you have striped two mirrors (RAID10 requires 4 disks), and you want to be able to replace failed disks easily.

My instincts tell me that triple mirrors, or hot spares, are likely to be operationally superior to using rsync.

mer mentions using partitions to manage vdev size. You can also use geom(8) concats to concatenate providers (read partitions) to make larger providers (read vdevs) -- but you have to apply some common sense.

Please tell us about the capacity of each disk including the drives you are considering for rsync.
 
If you're using a two pools mirror consisting of two mirrored drives each, you can also just use the 4 drives in a single mirror.
Same redundancy, but less complicated. No rsync is needed to synchronize data within a mirror. That's what ZFS does.
"Mirror" doesn't neccassarily mean "two drives." You can have any amount of drives in a mirror-pool - even one, even if that does not make much sense.
But the question is to find a reasonable compromise that's worth the situation.
What exactly are you going to achive?
You see, having a mirror of 4 drives, gives you a lot of safety (3 drives may fail) - against hardware failure, but cost you a lot of space (only the space of 1 drive available.) Also write and access speed will differ on the kind of RAID and the amount of drives. While your BU device may be slower, your drive/pool containing / and /var/ should be fast.
Setting up the 4 drives as a raidz2 pool, gives you also very good safety against hardware failure (2 drives may fail) but also more space (~2 drives) Adding a 5th drive could either add more space to a raidz2, or you can create a raidz3 (3 drives may fail.) But,
Question is: How much safety do you need for what?
A RAID system "only" protects you from hardware failure. But for being protected from the whole machine stolen or destroyed, e.g. by fire or a natural desaster, no amount of HW redundancy protects you from that. For that you need to have some additional BU space in another place, a second machine in the basement or outside your home, or webspace on a server in another country...
So, again the question: What kind of data needs to be how safe? And how much is it?
E.g. your porn collection may be safe enough on a single two drives mirror. But your source code repository, company's accounting files etc. better be saved on more than one machine, plus best having also some copies as encrypted tarballs on some webspace.
 
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