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

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

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.

The way I think of the options, raidz1 is less reliable and slower than 2-way mirrors, but can give you somewhat more capacity at 3 or more disks (but please don't use many unless you want to lose data).  2-way mirrors should resilver fastest when you have to replace a disk.  Raidz2 is more reliable to random failure than either of those (a checksum error while rebuilding isn't recoverable by 2-way mirror or raidz1), and if you have a larger number of disks (5+), raidz2 can give you more capacity than mirrors, but resilvers take longer, and performance is also less than mirrors.  If you want bulletproof and don't care about capacity, 3-way (or more) mirrors are also an option.  Raidz3 is basically a more resilient version of raidz2, with the same drawbacks.

Tim

________________________________
From: Harry Putnam <reader at newsguy.com>
Sent: Friday, November 6, 2020 6:30 PM
To: openindiana-discuss at openindiana.org <openindiana-discuss at openindiana.org>
Subject: Re: [OpenIndiana-discuss] what to setup with 4 matched disks

James via openindiana-discuss <openindiana-discuss at openindiana.org>
writes:

> On 01/11/2020 18:10, Harry Putnam wrote:
>
>> I've been coasting along for several years only using matched and
>> mirrored pairs of disks.
>>
>> Now I would like to do some experimenting with some of the other
>> possible setups.  I'm thinking maybe raidz2 or raidz3.
>
> How much data do you have?  For small amounts stick with mirrors.

Small potatoes.. maybe 4 TB total.  things are complicated a bit by
the fact that my HP xw8600 is not capable of running 3 TB or larger
discs.  And Is somewhat limited in ports, without some creative
cobbling.


> Do you own the HDDs already?  For 4TB of storage a mirror is about the
> same price as raidz because the price per capacity of HDDs goes up

Well as I mentioned in OP my experimenting is taking place on Vbox VM
where of course disc or limitied only by space on the HOST.

[...]

Something I'm not clear about.
This thread did not cover it..

Is there a big difference between 6 2 disk mirrors in 6 vdevs as
compared to 1 vdev of 3 sets of 2disk mirrors.

I haven't done the second method.  What all does it have going for it
over the multiple vdev case?

>
> "zfs mirror vs raidz":
> https://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/
> etc.

Good reading there, thanks.  Although I must admit I probably
understood no more than 60 maybe 65 percent.  I'm sure its more my
shortcoming than the authors. And I'm hope full about  that percentage
rising.
At my age that's always assuming the man with the scythe doesn't burst
upon the scene too quickly ... hehe


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