Re: ZFS on labelled partitions (was: Re: LSI SAS2008 mps driver preferred firmware version)
On Tue, Nov 17, 2015 at 12:08 AM, Patrick M. Hausen wrote: > Hi, all, > > > Am 16.11.2015 um 22:19 schrieb Freddie Cash : > > > > 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 Or is this just outdated folklore? > On Solaris, using raw devices allows ZFS to enable the caches on the disks themselves, while using any kind of partitioning on the disk forces the caches to be disabled. This is not an issue on FreeBSD due to the way GEOM works. Caches on disks are enabled regardless of how the disk is accessed (raw, dd-partitioned, MBR-partitioned, GPT-partitioned, gnop, geli, whatever). This is a common misconception and FAQ with ZFS on FreeBSD and one reason to not take any Sun/Oracle documentation at face value, as it doesn't always apply to FreeBSD. There were several posts from pjd@ about this back in the 7.x days when ZFS was first imported to FreeBSD. -- Freddie Cash fjwc...@gmail.com ___ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
Re: ZFS on labelled partitions (was: Re: LSI SAS2008 mps driver preferred firmware version)
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 wrote: > Hi, all, > > > Am 16.11.2015 um 22:19 schrieb Freddie Cash : > > > > 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 > -- > punkt.de GmbH * Kaiserallee 13a * 76133 Karlsruhe > Tel. 0721 9109 0 * Fax 0721 9109 100 > i...@punkt.de http://www.punkt.de > Gf: Jürgen Egeling AG Mannheim 108285 > > ___ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
