[OpenIndiana-discuss] what to setup with 4 matched disks

[Coalson, Timothy Scott (S&T-Student)]

Sorry, no I did not mean you could do 3-way mirror with 2 disks, you'd need 3 disks for that.  I had the impression you were looking to use 6 disks in one pool, and if you use 2-way mirrors, then that would imply 3 pairs of disks, that is where that 3 came from.

One pool can have multiple vdevs (and usually does for sizeable storage pools), and each vdev uses a fixed redundancy scheme - a mirror vdev is a byte-for-byte copy across all​ of its member disks, no matter how many members it has.  To get multiple 2-way mirror sets in a pool, you need multiple vdevs.

Tim

________________________________
From: Harry Putnam <reader at newsguy.com>
Sent: Monday, November 9, 2020 10:49 AM
To: openindiana-discuss at openindiana.org <openindiana-discuss at openindiana.org>
Subject: Re: [OpenIndiana-discuss] what to setup with 4 matched disks

Bob Friesenhahn <bfriesen at simple.dallas.tx.us> writes:

[...]

> With only a small number of disks (and to aid human comprehension when
> something goes wrong) I suggest using mirrors with a regular pool
> 'scrub' schedule.  With more disks raidz2 starts making sense but
> raidz2 is less flexible.

Thanks to all posters, lots of good input.

Sounds like I need to stay with my tried and true setup.

1 mirrored matched disc boot vdev, 2 mirrored vdevs of 2 disks each so 6 disks
making 3 pools in all.  rpool, p0, p1.

Someone (T Coalson)mentioned 3 way mirror with 2 disks.  I must admit
I do not understand how that is even possible.  I guess my concept of
mirror is stuck at 2 matched disks set as mirror, in a pool.

T Coalson wrote:

> By "1 vdev of 3 sets of 2disk mirrors", do you mean a vdev
> specification "mirror dev1 dev2 dev3 dev4 dev5 dev6"?  That doesn't
> make 2-way mirrors, it makes a 6-way mirror with usable capacity equal
> to one disk.  In zfs, "mirror" doesn't imply "pair".  I think what you
> were looking for is 3 mirror vdevs with 2 disks in each.

I'm afraid I'm really not understand this.  I had gotten the
impression somewhere that it was possible to have 3 different mirrors
each containing different data inside one vdev. (I've never tried
anything like that)

But, now that you drew that out a bit; what I was saying sounds
completely ridiculous.

I think I am still not understanding the concept of `mirror'.
3 way mirror with 2 disks does not fit my incorrect understanding at
all.

What I've ever actually done is install 3 pairs of matched disks and
created 3 pools from them.  (I meant `matched' in the sense of 2 disks
match each other (same brand, same size) in each pool, not that all
disks match each other).

And I'm currently experimenting (on VBox vm) with 1 matched pair of
boot disks in a 2 disk mirror, and 7 bigger matched disks in raidz2.  My first
try at anything but 2 disk mirrors.



_______________________________________________
openindiana-discuss mailing list
openindiana-discuss at openindiana.org
https://openindiana.org/mailman/listinfo/openindiana-discuss