linux-kernel - Re: Top 10 bugs/warnings for the week of March 23rd, 2008

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Message-ID: <20080526173848.GM32407@duck.suse.cz>
Date:	Mon, 26 May 2008 19:38:48 +0200
From:	Jan Kara <jack@...e.cz>
To:	Bart Van Assche <bart.vanassche@...il.com>
Cc:	Oliver Neukum <oliver@...kum.org>, Theodore Tso <tytso@....edu>,
	Ingo Molnar <mingo@...e.hu>, Jan Kara <jack@...e.cz>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Top 10 bugs/warnings for the week of March 23rd, 2008

On Mon 26-05-08 19:28:23, Bart Van Assche wrote:
> On Mon, May 26, 2008 at 7:09 PM, Oliver Neukum <oliver@...kum.org> wrote:
> > Am Montag 26 Mai 2008 19:01:48 schrieb Theodore Tso:
> >> If the USB stack folks would like to work on how to recognize that
> >> it's the same USB stick that had been previously pulled, so that it
> >> gets the same block device, and we can decide for how long we should
> >> keep dirty buffers around associated with a pulled USB stick, we can
> >> certainly have that conversation.  :-)
> >
> > Even if we could tell whether the device has remained the same, how
> > would we know the medium wasn't exchanged?
> 
> Looking at the filesystem UUID could help -- this is an ID that is
> present as data on the disk, and that is even independent of the bus
> type. See also /dev/disk/by-uuid.
  Yes, but as Oliver wrote if someone modified the filesystem in the mean
time, you won't notice it - UUID doesn't help here.

> For the journaling filesystems I am familiar with the default value
> for the commit parameter is 5 seconds. Would it be a good idea to
> leave the default to 5s for non-removable devices, and to change this
> default to 1s for removable devices ?
  I don't think it's a good idea:
1) You'd even more stress wear-leveling of USB flash drives - btw, given
their sizes it does not make much sence to use ext3 on your USB stick. I
still use VFAT/ext2 there.

2) You'd probably notice performance decrease because of more journaling
overhead.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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