Date: Tue, 17 Nov 2015 08:23:06 +0000 From: krad <kraduk@gmail.com> To: "Patrick M. Hausen" <hausen@punkt.de> Cc: Freddie Cash <fjwcash@gmail.com>, freebsd-scsi@freebsd.org, freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: ZFS on labelled partitions (was: Re: LSI SAS2008 mps driver preferred firmware version) Message-ID: <CALfReycoUnJagDTW79TQ1VP4AUO0pYT08EEQqx30UmWbpsOVDA@mail.gmail.com> In-Reply-To: <878D84A9-4553-413B-ACA4-5ABF499F28C1@punkt.de> References: <5644FF09.9090200@free.de> <CA%2BE3k93QrUFA3BvhoswkVDXh2bR2aLYG6Z0TOrisVvNL=%2BMZVA@mail.gmail.com> <56472686.5030301@free.de> <20151114143104.GA41119@in-addr.com> <7710CBCC-E68F-4454-9E29-E50ED1C6B511@sarenet.es> <CAN6yY1sH0PnnF_AGwDsA75i_Z6ptOr4J0c_Gqrt%2BRFO6eZsW-Q@mail.gmail.com> <CAOjFWZ4Js65gQZc6rbT9SKg-jZozziTa=JGpJys6HyejdgWP%2Bg@mail.gmail.com> <20151116205734.GM48728@zxy.spb.ru> <CAOjFWZ49A8b6g=mQL3jzJaNX-Lf%2BuDCvmscyB6F4tr7Ax=HMbg@mail.gmail.com> <878D84A9-4553-413B-ACA4-5ABF499F28C1@punkt.de>
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>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@punkt.de> wrote: > Hi, all, > > > Am 16.11.2015 um 22:19 schrieb Freddie Cash <fjwcash@gmail.com>: > > > > =E2=80=8BYou 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 possibl= e > downsides, because ZFS documentation explicitly states: > > ZFS operates on raw devices, so it is possible to create a storag= e > 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 > info@punkt.de http://www.punkt.de > Gf: J=C3=BCrgen Egeling AG Mannheim 108285 > >
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