Date: Sat, 25 Feb 2012 22:43:24 +0100 From: Peter Maloney <peter.maloney@brockmann-consult.de> To: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> Cc: freebsd-fs@freebsd.org Subject: Re: glabel, gpart and zfs confusion. Message-ID: <4F4955FC.6040308@brockmann-consult.de> In-Reply-To: <alpine.GSO.2.01.1202250943480.6378@freddy.simplesystems.org> References: <3E3E4094-77E2-490B-9574-5B95ECDED447@pean.org> <4F48A402.70009@brockmann-consult.de> <alpine.GSO.2.01.1202250943480.6378@freddy.simplesystems.org>
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Am 25.02.2012 16:56, schrieb Bob Friesenhahn: > On Sat, 25 Feb 2012, Peter Maloney wrote: > >> In Solaris, I've read that the IO system is designed such that a some >> commands (eg. flush of a partition) does not necessarily flush the >> disk's write cache... like the command can't move up the chain. So if >> you put zfs on a partition, you can get data loss (eg. transaction >> rollback required and probably no corruption). > > I wonder where you read that since it seems like bad information? In > Solaris, if zfs uses a partition (rather than the whole disk), the > disk write cache is not enabled by default due to the possibility that > some other partition uses a legacy filesystem like UFS, which could > become inconsistent and corrupted if the write cache is enabled. The > drawback then becomes that zfs writes are likely to incur more latency. No idea. I was just trying to point out where this recommendation to keep it separate comes from... but I don't know the details. But what you said makes sense. But I am sure that among the random things I read that sounded semi-credible (eg. by some guy claiming to be a ZFS engineer), it wasn't only about performance; it was more about corruption. (but then again, there are lots of doomsayers saying ZFS will somehow fail you, even though when they explain it, it is usually user error) And thanks for your criticism; looking back at this document: http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide It looks like they just talk about the cache and not corruption, even if I look at very old versions of the page. So either what I read before was likely quite wrong, or just opinion based eg. some bad experience of some tester or admin.
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