Date: Tue, 30 Sep 2008 11:40:50 +1000 From: Andrew Snow <andrew@modulus.org> To: freebsd-stable@freebsd.org Subject: Re: UNEXPECTED SOFT UPDATE INCONSISTENCY; RUN fsck MANUALLY Message-ID: <48E183A2.8000209@modulus.org> In-Reply-To: <5f67a8c40809290809j58639df8ka65184151161cab6@mail.gmail.com> References: <20080921213426.GA13923@0lsen.net> <20080921220720.GA9847@icarus.home.lan> <249873145.20080926213341@takeda.tk> <20080927051413.GA42700@icarus.home.lan> <765067435.20080926223557@takeda.tk> <20080927064417.GA43638@icarus.home.lan> <588787159.20080927003750@takeda.tk> <5f67a8c40809282030l7888d942q548d570cd0b33be9@mail.gmail.com> <20080929040025.GA97332@icarus.home.lan> <48E080C0.9070103@modulus.org> <5f67a8c40809290809j58639df8ka65184151161cab6@mail.gmail.com>
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Zaphod Beeblebrox wrote: > Also, there > exists data within the ARC (I'm always tempted to say the ARC Cache, but > that is redundant) that is also then in paging memory. OK, but one advantage of ZFS memory consumption is under heavy write loads, where much of the memory is used to store and reorder writes. The heavy memory consumption under reading is a shame, but ZFS has to cache and use more metadata than UFS, so its a price you pay for the extra features and benefits. What I think we need is a way to turn off read-caching except for metadata. This allows ARC to only be used more efficiently. Currently you can turn all read-ahead on or off, with the provided sysctl tunables, but would be easy to implement a metadata-only option. I found that access speed suffers when metadata is not prefetched. If you are running an X workstation with 2GB or less memory, then I agree ZFS is a bad default choice. For my workstation I would still use ZFS, I would: * turn down ARC size, * turn off read-ahead except for metadata, * and even turn off ZIL and write cache flushing, which solves the annoyance of unpredictable delays when flushing buffers. Not a good choice for a server but perfect for a workstation. - Andrew
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