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authorChristoph Hellwig <hch@lst.de>2015-01-21 13:40:00 +0300
committerChristoph Hellwig <hch@lst.de>2015-02-05 16:35:18 +0300
commit8650b8a058502d6957ba13dfb5544724fa038118 (patch)
tree38b0135cf5f5692e5f766332b8470ef9050e7980 /Documentation/filesystems/nfs
parent7fbc1067f06098c6b674e672fbb17e758fcc9402 (diff)
downloadlinux-8650b8a058502d6957ba13dfb5544724fa038118.tar.xz
nfsd: pNFS block layout driver
Add a small shim between core nfsd and filesystems to translate the somewhat cumbersome pNFS data structures and semantics to something more palatable for Linux filesystems. Thanks to Rick McNeal for the old prototype pNFS blocklayout server code, which gave a lot of inspiration to this version even if no code is left from it. Signed-off-by: Christoph Hellwig <hch@lst.de>
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+pNFS block layout server user guide
+
+The Linux NFS server now supports the pNFS block layout extension. In this
+case the NFS server acts as Metadata Server (MDS) for pNFS, which in addition
+to handling all the metadata access to the NFS export also hands out layouts
+to the clients to directly access the underlying block devices that are
+shared with the client.
+
+To use pNFS block layouts with with the Linux NFS server the exported file
+system needs to support the pNFS block layouts (currently just XFS), and the
+file system must sit on shared storage (typically iSCSI) that is accessible
+to the clients in addition to the MDS. As of now the file system needs to
+sit directly on the exported volume, striping or concatenation of
+volumes on the MDS and clients is not supported yet.
+
+On the server, pNFS block volume support is automatically if the file system
+support it. On the client make sure the kernel has the CONFIG_PNFS_BLOCK
+option enabled, the blkmapd daemon from nfs-utils is running, and the
+file system is mounted using the NFSv4.1 protocol version (mount -o vers=4.1).
+
+If the nfsd server needs to fence a non-responding client it calls
+/sbin/nfsd-recall-failed with the first argument set to the IP address of
+the client, and the second argument set to the device node without the /dev
+prefix for the file system to be fenced. Below is an example file that shows
+how to translate the device into a serial number from SCSI EVPD 0x80:
+
+cat > /sbin/nfsd-recall-failed << EOF
+#!/bin/sh
+
+CLIENT="$1"
+DEV="/dev/$2"
+EVPD=`sg_inq --page=0x80 ${DEV} | \
+ grep "Unit serial number:" | \
+ awk -F ': ' '{print $2}'`
+
+echo "fencing client ${CLIENT} serial ${EVPD}" >> /var/log/pnfsd-fence.log
+EOF