Hi Luke,
Luke Schwab wrote:
Hi,
In migrating from **VM to ZFS am I going to have an issue with Major/Minor
numbers with NFS mounts? Take the following scenario.
1. NFS clients are connected to an active NFS server that has SAN shared
storage between the active and standby nodes in a cluster.
2. The NFS clients are using the major/minor numbers on the active node in the
cluster to communicate to the NFS active server.
3. The active node fails over to the secondary node in the cluster.
4. The NFS clients can no longer access the same major minor number for NFS shares.
AFAIK NFS uses the fsid provided by the underlying FS to identify the
file system.
Most of the underlying filesystems use major/minor number as the fsid
(as reported by stat(2))...
ZFS creates a unique FSID for every filesystem (called a object set in
ZFS terminology).
The following is the stack trace which shows how we create a unique id
when a new FS is created :
-- snip --
# zfs create mypool/test
-- snip --
# dtrace -n 'fbt::unique_create:entry { stack(); ustack()}'
dtrace: description 'fbt::unique_create:entry ' matched 1 probe
CPU ID FUNCTION:NAME
1 38106 unique_create:entry
zfs`dsl_dataset_create_sync+0x10e
zfs`dmu_objset_create_sync+0x42
zfs`dsl_dir_sync+0x47
zfs`dsl_pool_sync+0xd4
zfs`spa_sync+0x110
zfs`txg_sync_thread+0x1a5
unix`thread_start+0x8
-- snip --
The unique id is saved (ondisk) as part of dsl_dataset_phys_t in
ds_fsid_guid.
And this id is a random number generated when the FS is created.
This id is used to populate the zfs_t structure (refer to zfs_init_fs()).
And the same id would be used as FSID for NFS.
Hope that answers your questions.
-- Sanjeev.
Does anyone know how ZFS fixes this problem. I read something on NFSv4 in Linux that has
the "fsid" option of mount that allows you to set the device name instead of
the major/minor number. Does Solaris 10 have anything like this?
Thanks,
ljs
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