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mounting with sync?

To: Linux xfs mailing list <linux-xfs@xxxxxxxxxxx>
Subject: mounting with sync?
From: Joshua Baker-LePain <jlb17@xxxxxxxx>
Date: Tue, 11 Jun 2002 14:03:25 -0400 (EDT)
Sender: owner-linux-xfs@xxxxxxxxxxx
In the course of trying to track down some disk performance issues, I'm 
trying to mount an XFS partition on a (slow) SCSI disk synchronously via 
the fstab entry:

/dev/sda1               /mnt/test               xfs     logbufs=8,sync  0 0

However, I'm not getting the behavior I would expect:

[root@brian root]# time dd if=/dev/zero of=/mnt/test/bigfile bs=1024k 
count=512; time umount /mnt/test
512+0 records in
512+0 records out

real    0m57.848s
user    0m0.000s
sys     0m3.280s

real    1m6.472s
user    0m0.000s
sys     0m0.610s

So the 'dd' returns after 1 minute, but it takes it another minute to 
actually unmount the partition (during which there is lots of writing 
going on).  I tried adding 'osyncisdysnc', which ISTR is the default now, 
and it (obviously) didn't help.

Am I misinterpreting what's going on here?  Is this the expected behavoir?
The kernel is 2.4.18 from the 1.1 release.


Joshua Baker-LePain
Department of Biomedical Engineering
Duke University

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