From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Chester R. Hosey" Subject: Re: Less disk space with reiser4? Date: Mon, 11 Apr 2005 16:43:28 -0400 Message-ID: <425AE170.7010806@nauticom.net> References: <425A8A1D.9040206@siwnet.net> <20050411195253.GD6211@backtop.namesys.com> <425ADC6C.8090209@namesys.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: <425ADC6C.8090209@namesys.com> List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: reiserfs-list@namesys.com Many filesystems claim degraded performance as free space decreases beyond a certain threshold. However, they often allow the user to exceed this point and accept the decline in performance. While Alex's explanation does well to explain why a certain amount of free space is required in the case of a commit depending on a certain amount of free space, it doesn't quite show that 45 gigs are required to cover this requirement on a terabyte of space. Is this a reasonable requirement? Can we get a FAQ entry on namesys.com which addresses this additional overhead imposed by V4 (including whether this is a permanent thing, or whether future revisions will likely reduce the overhead)? Hans Reiser wrote: > Alex Zarochentsev wrote: > > >>On Mon, Apr 11, 2005 at 04:30:53PM +0200, Stefan Andersson wrote: >> >> >> >>>Hi, >>> >>>I have a disk array wich I used reiserfs(v3) on, and got 932G. >>>Now I started to test reiser4 on it and get less space, 886G. >>> >>>Is it suppose to be like this or is there something wrong? >>> >>> >> >>reiser4 reserves 5% of disk space. >> >>That is so because of delayed block allocation impelented in reiser4. Actual >>block allocation is done near the transaction commit, it means the allocation >>has to be reliable -- we can't return ENOSPC because the write(2) call when we >>could return an error was already completed successfully. >> >>The reserved space makes the allocation reliable because it covers possible >>insertions (and growing of the internal reiser4 tree) of new extent items >>insertions on a highly fragmented fs. >> >> > > It also improves performance to ensure that at least 5% is free. > > >> >> >> >>>I'am using linux 2.6.11.4 and default settings for mkfs.reiser4 and >>>mkfs.reiserfs, >>>and reiser4 patch from 2.6.11-mm3. >>> >>>//Stetan >>> >>> >>> >> >> >> > >