freebsd-questions Digest, Vol 760, Issue 6

Dave B g8kbvdave at
Fri Jan 4 16:14:11 UTC 2019

Understood re what ZFS can do, much the same as high end hardware
controllers with their own embedded software (BIOS) then.  (I forget the
make/model, but I know that one card cost well over twice what the rest
of the server machine cost when new!)

Only know that, as in it's original life, one of the drives went sick
fairly early in it's life so needed replacing.  After it was replaced,
and a lot of boot time scary messages, it rebuilt the RAID all by
itself, then booted as if nothing had happened!   Neat!.


    Dave B.

On 04/01/2019 15:57, Kevin P. Neal wrote:
> On Fri, Jan 04, 2019 at 03:43:06PM +0000, Dave B via freebsd-questions wrote:
>> Have to ask, if, IF the BIOS is handling the existing RAID itself, why
>> can't FreeBSD handle the result just like a single drive?  Of course, if
>> some tool/driver loaded at boot time by the old OS is doing it, then
>> it's toast in any case.
> If the array is presented to FreeBSD as a single drive then FreeBSD is more
> than able to use it as a single drive. 
> But ZFS wouldn't be able to provide the error correction that it provides
> when ZFS manages the array itself. ZFS does checksumming, and if a block
> is corrupted then ZFS wants to be able to reconstruct the bad block. But
> if ZFS isn't managing the array then ZFS can't do this reconstruction.
> You can somewhat work around that by setting the copies=2 option, but that
> cuts your available space in half due to duplicating every block of data.
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