Re: (reiserfs) Re: LVM / Filesystems / High availability

Florian Lohoff (flo@quit.mediaways.net)
Thu, 25 Jun 1998 12:01:13 +0200

On Thu, Jun 25, 1998 at 01:33:42AM +0200, Erik Corry wrote:
> In article <199806241751.NAA10373@dcl.MIT.EDU> you wrote:
>
> > OK, suppose I have a 54 terrabyte filesystem, with all PE's in use, and
> > I need to remove a 9 gigabyte disk from the middle of the filesystem,
> > because it's failing.
>
> > I can't do (2) because I don't have a spare PE to use.
>
> > I could do (1) but that would mean temporarily copying *more* data to
> > the failing 9 gigabyte disk as part of the compaction process, thus
> > putting that data at risk.
>
> This is a rather special situation, with hardware failing,
> and a bad basis for design decisions. Normally in the
> kernel we assume that the hardware works. If you want to
> guard against that, then you can use more advanced RAID
> features. If your disk is failing, perhaps you should be
> getting the backup tapes out of the fireproof safe anyway.

This IS a very special situation but most of the guys
using this kind of setup are already using mirrors or
raid5 or have at least a spare disk to connect that you
might just conect to the VG and copy all data ...
I think we can live with this problem ...

> > If the filesystem is LVM aware, and is using structed block addresses,
> > then all it needs to do is to stop allocating blocks in that particular
> > PE, and start vacating blocks and inodes out of the failing disk to
> > others, on-line. This is faster and more robust.
>
> Sounds like a messy non-solution, where real solutions
> (RAID, backups) exist. No serious HA-solution is going to
> be based on "If the disk starts failing, then get as much
> data as possible off it before it blows up entirely".

Agree ..

Flo

-- 
Florian.Lohoff@mediaWays.net			+49-5241-80-7085
aka flo@mini.gt.owl.de			@HOME	+49-5241-470566


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