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2pNFS block layout server user guide
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4
5The Linux NFS server now supports the pNFS block layout extension.  In this
6case the NFS server acts as Metadata Server (MDS) for pNFS, which in addition
7to handling all the metadata access to the NFS export also hands out layouts
8to the clients to directly access the underlying block devices that are
9shared with the client.
10
11To use pNFS block layouts with with the Linux NFS server the exported file
12system needs to support the pNFS block layouts (currently just XFS), and the
13file system must sit on shared storage (typically iSCSI) that is accessible
14to the clients in addition to the MDS.  As of now the file system needs to
15sit directly on the exported volume, striping or concatenation of
16volumes on the MDS and clients is not supported yet.
17
18On the server, pNFS block volume support is automatically if the file system
19support it.  On the client make sure the kernel has the CONFIG_PNFS_BLOCK
20option enabled, the blkmapd daemon from nfs-utils is running, and the
21file system is mounted using the NFSv4.1 protocol version (mount -o vers=4.1).
22
23If the nfsd server needs to fence a non-responding client it calls
24/sbin/nfsd-recall-failed with the first argument set to the IP address of
25the client, and the second argument set to the device node without the /dev
26prefix for the file system to be fenced. Below is an example file that shows
27how to translate the device into a serial number from SCSI EVPD 0x80::
28
29	cat > /sbin/nfsd-recall-failed << EOF
30
31.. code-block:: sh
32
33	#!/bin/sh
34
35	CLIENT="$1"
36	DEV="/dev/$2"
37	EVPD=`sg_inq --page=0x80 ${DEV} | \
38		grep "Unit serial number:" | \
39		awk -F ': ' '{print $2}'`
40
41	echo "fencing client ${CLIENT} serial ${EVPD}" >> /var/log/pnfsd-fence.log
42	EOF
43