ZFS on labelled partitions (was: Re: LSI SAS2008 mps driver preferred firmware version)

[krad]

>From what i remember its a  control thing. If you have another layer below
zfs, be it software based or hardware based, zfs cant be sure what is going
on, therefore cant guarantee anything. This is quite a big thing when it
comes to data integrity which is a big reason to use zfs. I remember having
to be very careful with some external caching arrays and making sure that
they flushed correctly as often they ignore the scsi flush commands. This
is one reason why I would always use the IT based firmware rather then the
RAID one, as its less likely to lead to issues.

On 17 November 2015 at 08:08, Patrick M. Hausen <hausen at punkt.de> wrote:

> Hi, all,
>
> > Am 16.11.2015 um 22:19 schrieb Freddie Cash <fjwcash at gmail.com>:
> >
> > ​You label the disks as they are added to the system the first time.
> That
> > way, you always know where each disk is located, and you only deal with
> the
> > labels.
>
> we do the same for obvious reasons. But I always wonder about the possible
> downsides, because ZFS documentation explicitly states:
>
>         ZFS operates on raw devices, so it is possible to create a storage
> pool comprised of logical
>         volumes, either software or hardware. This configuration is not
> recommended, as ZFS works
>         best when it uses raw physical devices. Using logical volumes
> might sacrifice performance,
>         reliability, or both, and should be avoided.
>
> (from http://docs.oracle.com/cd/E19253-01/819-5461/gbcik/index.html)
>
> Can anyone shed some lght on why not using raw devices might sacrifice
> performance or reliability? Or is this just outdated folklore?
>
> Thanks,
> Patrick
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