Adding disks to a Raid-Z1 pool
reddit / freebsd

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[deleted] · 2020-08-21 04:03

[deleted]

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hedgehogentry · 2020-08-21 04:35

You can add vdevs to a pool, but the data will not be rebalanced which
is not optimal from a performance or redundancy point of view. I
suppose you could rebalance it by copying your old datasets new
datasets and deleting the old datasets. I have not tested that though.

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rhavenn · 2020-08-21 04:43

ZFS pools are made up of 1 or more vdevs. You can’t expand a vdev. You
can NOT remove vdevs either. However, you can add a vdev to a pool.

Technically, you could add a single disk vdev to an existing pool, but
that becomes a single point of failure. You lose a vdev and you lose
the pool. So, each vdev has to be able to stay consistent on its own,
but the sum total of your vdevs makes up the pool.

It’s recommended for balance purposes to add vdevs of the same disk
number, so when you’re ready to grow you’ll add another 3 disk raidz1
vdev. You could add a 2 disk mirror vdev and when you get another disk
add the 3rd and 4th disks as an additional mirror vdev. Best
performance, but not space optimal. It’s up to you.

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bro_can_u_even_carve · 2020-08-21 08:31

ZFS doesn't really support adding one drive at a time very well. It's
one of its few "downsides," at least for home use. I guess this is why
people use stuff like unraid.

An even bigger problem is that raidz1, like RAID-5, should never be
used with drives larger than 1TB or so. The reason is that with large
drives, the risk of a second drive failing during the resilver is very
high. At that point your pool (or array) is toast.

There isn't a good option for using three disks, I'm afraid. Your best
bet is 4 drives for a stripe of two mirrors (the ZFS version of
RAID-10), or 6 drives for raidz2.

The striped mirror pool can be expanded by two drives (a mirrored
pair) at a time. To "expand" a raidz2 pool, your best bet is to add a
second raidz2 vdev to it... so six more drives.

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mithrenithil · 2020-08-22 10:39

So this isn't specifically a ZFS solution, but more of a way of
thinking about management of storage and growth.

Rather then thinking that you will create a storage device which will
last you forever, instead plan to add more pools to the NAS.

This will allow you to copy/migrate your existing data to the new
pool.  With ZFS's checksuming  you are in essence doing a data
integrity check each time you do this.

Then you can re-purpose your old pool, or the disks themselves after
you have done a health check on them.

This is specifically based on disks getting cheaper and better over
time.

Just to note I'm talking about multi year plan here, and I have no
idea how long \~15TB would last you :)

Personally I tend to use old storage devices for "meh" archiving or
for my backup devices.