linux-kernel - Re: Reiser4. BEST FILESYSTEM EVER.

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Message-ID: <14921.1175967598@turing-police.cc.vt.edu>
Date:	Sat, 07 Apr 2007 13:39:58 -0400
From:	Valdis.Kletnieks@...edu
To:	johnrobertbanks@...tmail.fm
Cc:	Jan Harkes <jaharkes@...cmu.edu>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Reiser4. BEST FILESYSTEM EVER.

On Fri, 06 Apr 2007 19:47:36 PDT, johnrobertbanks@...tmail.fm said:
> On Fri, 6 Apr 2007 11:21:19 -0400, "Jan Harkes" <jaharkes@...cmu.edu>

> > With compression there is a pretty high probability that one corrupted
> > byte or disk block will result in loss of a considerably larger amount
> > of data. 
> 
> Bad blocks are NOT dealt with by the filesystem,... so your comment is
> irrelevant, or just plain wrong.
> 
> If your filesystem is writing to bad blocks, then throw away your
> operating system.

You know... occasionally, blocks go bad *after* you write to them.  If
you have an uncompressed filesystem, it's often possible to recover most
of the file , and just have a few 512-byte blocks of zeros, simply by
doing something like 'dd if=bad.file of=bad.file bs=512 conv=noerror'
or careful applications of 'skip=N'.  If it's compressed, you usually
can't recover the rest of a compression group if a previous block is lost.

(And for those who talk about backups - yes, taking backups is good.
However, it's the rare laptop or desktop machine that can afford the
luxury of RAID disks, and backups usually happen once a night, if that
often.  This means that if you've been working hard on something important
all day, and the disk blows chunks at 4:30PM, you *will* be suddenly very
concerned over exactly how much you can recover off the failing drive....

And yes, I'd *love* to have all my users connected to nice SAN systems that do
snapshotting and remote replication to DR sites and all that - but have you
ever *priced* a petabyte of SAN storage, the NAS gateways to serve it to users,
and upgrading several tens of thousands of network ports to Gig-E? Hint -
US$1M would get us through a pilot, and probably $5M and up to *start*
deployment. Anybody wanna buy us an EMC DMX-3? :)

http://www.emc.com/products/systems/symmetrix/DMX_series/DMX3.jsp

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