[clug] mount(8) async/sync options

Martin Pool mbp at sourcefrog.net
Sat Jun 19 23:22:14 GMT 2004

On 20 Jun 2004, Ian Matters <ian at iristech.com.au> wrote:
> Can someone clarify the exact effect of the async and sync options in 
> the mount command please.
> I have been getting occasional complete machine lockups in my Debian 
> Testing based Xandros 2.0 machine when copying large amounts of files to 
> or from my USB 2.0 connected external hard drive.  It seems that using 
> the "sync" mount option fixes the problem.

Mounting it 'sync' means the data is written to the flash card
(almost?) immediately after it's written in userspace.  Mounting it
async means there is a write buffer.  The buffer is completely flushed
by sync(8) or umount.  Since flash is so slow the difference is
extreme.  I often have to wait over a minute for it to finish writing
things out.

If the kernel hangs if you don't use 'async' then you ought to report
the bug.  If it is a distro kernel report it to the distro; otherwise
to the USB Storage maintainer.

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