[lkml]   [2007]   [Feb]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [ANNOUNCE] DualFS: File System with Meta-data and Data Separation
Hi Jörn,

On Wed, 21 Feb 2007, [utf-8] Jörn Engel wrote:

> On Wed, 21 February 2007 05:36:22 +0100, Juan Piernas Canovas wrote:
>>> I don't see how you can guarantee 50% free segments. Can you explain
>>> that bit?
>> It is quite simple. If 50% of your segments are busy, and the other 50%
>> are free, and the file system needs a new segment, the cleaner starts
>> freeing some of busy ones. If the cleaner is unable to free one segment at
>> least, your file system gets "full" (and it returns a nice ENOSPC error).
>> This solution wastes the half of your storage device, but it is
>> deadlock-free. Obviously, there are better approaches.
> Ah, ok. It is deadlock free, if the maximal height of your tree is 2.
> It is not 100% deadlock free if the height is 3 or more.
> Also, I strongly suspect that your tree is higher than 2. A medium
> sized directory will have data blocks, indirect blocks and the inode
> proper, which gives you a height of 3. Your inodes need to get accessed
> somehow and unless they have fixed positions like in ext2, you need a
> further tree structure of some sorts, so you're more likely looking at a
> height of 5.
> With a height of 5, you would need to keep 80% of you metadata free.
> That is starting to get wasteful.
> So I suspect that my proposed alternate cleaner mechanism or the even
> better "hole plugging" mechanism proposed in the paper a few posts above
> would be a better path to follow.

I do not understand. Do you mean that if I have 10 segments, 5 busy and 5
free, after cleaning I could need 6 segments? How? Where the extra blocks
come from?


D. Juan Piernas Cánovas
Departamento de Ingeniería y Tecnología de Computadores
Facultad de Informática. Universidad de Murcia
Campus de Espinardo - 30080 Murcia (SPAIN)
Tel.: +34968367657 Fax: +34968364151
PGP public key:

*** Por favor, envíeme sus documentos en formato texto, HTML, PDF o PostScript :-) ***
 \ /
  Last update: 2007-02-21 19:35    [W:0.070 / U:0.068 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site