Re: sysinstall, GJOURNAL and ZFS

> Date: Tue, 9 Jun 2009 19:32:30 +0200 (CEST)
> From: Wojciech Puchar <wojtek_at_wojtek.tensor.gdynia.pl>
> Sender: owner-freebsd-current_at_freebsd.org
> 
> >> UFS2+SoftUpdates works fine on properly configured UFS2 - and very fast.
> > Yes, UFS2+SoftUpdates is very fast, however, in the case of a power
> > loss or having to pull the plug on a locked up system, it has a
> > noticeably higher chance of leaving you with an unbootable system than
> 
> can you please give an example how it may render unbootable system?
> 
> For what i know and ever used (ext2,ext3,reiserfs,rarely NTFS, UFS) 
> UFS is the only one that never failed. It is always recoverable, with few 
> lost files worst case.
> 
> I recommend you to read a paper about softupdates to understand why they 
> are so good.
> 
> The only problem with millions of files may be long fsck. but not THAT 
> long, and FreeBSD doesn't crash every day.

Not quite true. The problem is not soft updates. It is write cache on
many cheaper hard drives. While soft updates orders write to the hard
drive so that the only thing that you can lose is recently written
files, but soft updates depends on the data actually being written in
the proper sequence and SCSI disks and some ATA drives do this
correctly, but many don't and provide on tool to be really sure that
they have.

Of course, write cache can be disabled on ATA drives and that will make
soft updates safe, but the performance hit can be huge.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman_at_es.net			Phone: +1 510 486-8634
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