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Re: [zfs-discuss] Size discrepancy (beyond expected amount?)

Subject: Re: [zfs-discuss] Size discrepancy beyond expected amount?
Date: Fri, 20 Mar 2009 11:24:49 -0600

Bob F. has give you some excellent advice about using mirrored
configurations. I can answer your RAIDZ questions but your original
configuration was for a root pool and non-root pool using 4 disks

Start with two mirrored pools of two disks each. In the future,
you will be able to add two or more disks to your non-root pool.
You can't do that with a RAIDZ pool.

If you need to, you can even detach one side of the mirror
of each pool. You can't do that with a RAIDZ pool. If you need
larger pools you can replace all the disks in both pools with
larger disks. You can do that with a RAIDZ pool, but more
flexibility exists with mirrored pools.

1. Yes, sensible.
2. Saving space isn't always the best configuration.
3. I don't know.
4. Yes, with more disks, you can identify hot spares to
be used in the case of a disk failure.


[email protected] wrote:
[email protected] writes:

So is 5 with 1 hotswap (total 6) a sensible arrangement? And would
that leave me with something like 2tb (minus manufacturer exaggeration)
and one disk would be swallowed for parity data.

Yeah, yeah.  Perhaps you can ask the "SI" to change the definition of
"T" from 10^12 to 2^40. The only people who are weird are those computer people who believe that 1K == 1024 and 1M is 2^20, etc. I suggested that we just give it a rest. (Even Flash memory is now "SI" measured)

I was only trying to forstall other posters pointing out that I really
didn't get 500gb on a 500gb disk.

But Casper, what about any of the 4 questions asked:

1) Is 5 disk raidz1 with 1 hotswap a sensible arrangemnt
2) Why is a 4 disk raidz1 not a good plan?  Isn't it still a space
   saving over 4 disks of mirror?  Or is the needed hotswap disk
   (bringing the total to 5) the deal breaker?
3) Is mixing same size IDE and SATA disks in a raidz1 a bad idea?
4) If all controllers are full, how is a hotswap added to a zpool? Just pull one of the zpool raidz1 disks out or what?

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