[OpenIndiana-discuss] Recommendations for fast storage

[Jim Klimov]

On 2013-04-17 21:25, Jay Heyl wrote:
> It (finally) occurs to me that not all mirrors are created equal. I've been
> assuming, and probably ignoring hints to the contrary, that what was being
> compared here was a raid-z2 configuraton with a 2-way mirror composed of
> two 8-disk vdevs. I now realize you're talking about 8 separate 2-disk
> mirrors organized into a pool. "mirror x1 y1 mirror x2 y2 mirror x3 y3..."


Well, to help you clarify things, there are simple mirrors made over
two identically sized storage devices (for simplicity, we won't go
into three- or four-way mirrors which are essentially the same idea
spread over more devices for higher reliability and read performance).

If you involve more couples of devices, you can build (in traditional
RAID terminology) either raid10 - one striping over many separate
mirrors, or raid01 - one mirror over two individual stripes (or plain
concatenations sometimes). While the performance is similar and
difference seems semantical, there is some. Most importantly, a
single broken disk in a stripe invalidates it, and thus a whole
half of raid01 top-level mirror becomes broken. That's why these
setups are rarely used nowadays, and ZFS didn't even bother to
implement them (unlike raid10) :)

HTH,
//Jim