From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressed by kernelnewbies.org regarding reiser4 inclusion] Date: Tue, 01 Aug 2006 10:24:49 +0300 Message-ID: <44CF01C1.9070802@argo.co.il> References: <20060801064837.GB1987@thunk.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: <20060801064837.GB1987@thunk.org> List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Theodore Tso Cc: David Lang , David Masover , tdwebste2@yahoo.com, Nate Diller , Adrian Ulrich , "Horst H. von Brand" , ipso@snappymail.ca, reiser@namesys.com, lkml@lpbproductions.com, jeff@garzik.org, linux-kernel@vger.kernel.org, reiserfs-list@namesys.com Theodore Tso wrote: > > Ah, but as soon as the repacker thread runs continuously, then you > lose all or most of the claimed advantage of "wandering logs". > Specifically, the claim of the "wandering log" is that you don't have > to write your data twice --- once to the log, and once to the final > location on disk (whereas with ext3 you end up having to do double > writes). But if the repacker is running continuously, you end up > doing double writes anyway, as the repacker moves things from a > location that is convenient for the log, to a location which is > efficient for reading. Worse yet, if the repacker is moving disk > blocks or objects which are no longer in cache, it may end up having > to read objects in before writing them to a final location on disk. > So instead of a write-write overhead, you end up with a > write-read-write overhead. > There's no reason to repack *all* of the data. Many workloads write and delete whole files, so file data should be contiguous. The repacker would only need to move metadata and small files. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.