Re: journal size reiserfs vs reiser4

["Vladimir V. Saveliev" <vs@namesys.com>]

Hello

michael chang wrote:
> On 9/1/05, Peter Staubach <staubach@redhat.com> wrote:
>>Hans Reiser wrote:
>>
>>>Research for filesystems generally says that as you get more than 85%
>>>full the performance goes down, by a lot as you get close to 100%.  5%
>>>is probably too little rather than too much.
>>>
>>Wow.  What is all that space used for? 

Reiser4 allocates log records dynamically. So it has to allocate some disk space even when it is about to remove a file.
Reserved space is used when allocation is required to preform removal operation.
This allows to avoid returning ENOSPC on operations which are usually used to free disk space.

 Other journalling file systems that
>>I have seen have limited things like journals to a much smaller space,
>>expressed in megabytes, and a much smaller number than thought originally.
>>The bigger journals just didn't end up adding to the performance measurably
>>and were just considered to be a waste of space that could be used more
>>usefully.
>>
> 
> Block-allocation efficiency.  Mainly to prevent super extreme
> fragmentation of even the smallest files, and to give enough room to
> do something that looks like repacking/defragmentation.
> 
> If you want to do repacking w/o 15-25%+ free space, then you're pretty
> much looking at the kind of algorithm found in Windows 9x
> (semi-offline defragment, and arrange blocks one at a time); online
> repacking is painful without much free space (often you have to
> repeatedly re consolidate the free space, which kinda messes things
> up).
> 
> Of course, for me personally, Reiser4 will be about 20 times more
> useful if it's a 40 GB disk and I can fill it up to 99% and defragment
> it completely within 12 hours or so, with maybe 10-20 files which are
> 275 MBs in size.  Win XP and sure NTFS couldn't do it, even with
> proprietary defragmenters...
>