[OpenIndiana-discuss] 800GB in 6 discs - 460GB in raidz

[Harry Putnam]

I continue to have a problem understanding the output of zfs list.

I've googled up a couple of what seem to be thorough explainations but
somehow am still not getting it.

Or maybe this is just what it looks like, that is, a lot of space gone
to parity striping.

   Name    USED    AVAIL   REFER   MOUNTPOINT
   p0      142k    460G    34.9    /z

No filesystems created yet, but the available column is apparently
saying there is a total of 460 GB of space available.

Ok, if that is correct then it means that 6 disks when totalled
individually adding up to 800+ GB has been reduced by nearly half to
accomodate raidz.

This is an install on a vbox vm.  I created 6 more discs beyond 2 for
a mirrored rpool.

The extra discs are a temporary setup to hold some data off an install
of oi 151_9 that I am about to do a fresh install of hipster on.

I have some 420+ gb of installed vms on the hardware host.

On the vm, I've created discs like so:

2 @  96G
2 @ 116G
2 @ 216G

There was no rhyme or reason to the sizing.. some have been in place
for a while so I broke up a mirrored pair and destroyed all fs and the
zpool on it.  Then just started adding discs in 100GB increments.

So, a total of roughly 854G

Less whatever for various things... but small amounts.  If used
individually.

So, in round figures it loses 50 % of available space in raidz
config.

I have no experience with raidz and have only ever mirrored paired
discs.

I put these discs in raidz in a effort to get a little more out of the
total space.  But in fact got very very little more space.

I guessed that I would be left with around 600 GB of space.... based
on a wag only.

This is all assuming I haven't made some boneheaded mistake or am
suffering from a boneheaded non-understanding of what `zfs list' tells
us.

Apparenly raidz does not really save enough space to make it worth
doing.  That is, in a space for config sense.  Nothing really gained
over just paired mirrors.