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NFS Issues with filesystem migration

To: linux-xfs@xxxxxxxxxxx
Subject: NFS Issues with filesystem migration
From: "Giddings, Bret" <bret@xxxxxxxxxxx>
Date: Fri, 14 Sep 2001 11:57:12 +0100
Sender: owner-linux-xfs@xxxxxxxxxxx
We are looking to migrate some existing advfs partitions on Compaq Tru64
Unix 4.0e to xfs partitions on linux and have observed extremely weird
problems in copying the files. The different scenarios and outcomes are
outlined below.

Test environment

Linux Server: Dell PowerEdge 4400 with hardware RAID on aacraid driver. OS
RedHat71. Tried with both SGI supplied kernels and 2.4.9 kernels.

Alpha Server: AlphaStation 200, Compaq Tru64 4.0e

Tar: Gnu tar on both systems (sym link on linux to /bin/tar to provide same
calling convention).

Test data: ex-users data - contains mix of usual stuff

TEST 1 - XFS

The xfs file system is NFS mounted on Alpha (push from the Alpha)

# cd /Ufs/servbg/users
# /bin/gnutar cfS - test | (cd /mnt/users; /bin/gnutar xpfS - )

Result: test directory expands from 21987 on advfs to 86224 on xfs (also,
the size of the data is initially higher and drops to this value a short
time after the copy is finished).

TEST 2 - XFS

The advfs file system on the Alpha is NFS mounted on the Linux machine (pull
from the Linux box).

# cd /mnt/users
# /bin/gnutar cfS - test | (cd /Ufs/servb00/users; /bin/gnutar xpfS -)

Result: test directory expands from 21987 on advfs to 23860 on local xfs
partition /Ufs/servb00 - this is probably a result of the differing block
sizes so OK.

TEST 3 - EXT2

The ext2 file system is NFS mounted on Alpha (push from the Alpha)

# cd /Ufs/servbg/users
# /bin/gnutar cfs - test | (cd /mnt; /bin/gnutar xpfS - )

Result : test directory contracts from 21987 on advfs to 21714 on ext2

TEST 4 - EXT2

The advfs file system on the Alpha is NFS mounted on the Linux machine (pull
from the Linux box).

# cd /mnt/users
# /bin/gnutar cfS - test | (cd /tmp; /bin/gnutar xpfS -)

Result: test directory contracts from 21987 on advfs to 21313 on ext2

PROBLEMS:

The most worrying problem for us is that remotely mounting an XFS directory
to a non-linux machines appears to result in quite excessive use of
diskspace. Looking at the test data, we found that (for example), a
.netscape/cache directory would grow from 9M to 33M. Is this type of
behaviour a known problem and is it likely to bite during normal operation
of the filesystem when nfs-mounted.

The usage reported by du on the linux server for the test directory shows
erratic value. During the copy, it rises to a higher value and then
decreases a bit - this seems counter intuitive. Indeed, different runs with
the same test data would show slight variations in resultant disk space used
for TEST 1.

thanks in advance,

Bret
--
Bret Giddings, Systems Manager, Computing Service, University of Essex
Tel: (01206) 872577     Email: bret@xxxxxxxxxxx      Fax: (01206) 860585


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