hi,
my name is guy keren, and the company i work at is looking at
implementing an NFS 4.1 server for our existing storage product.
during the design, we encountered some issues with high-availability and
persistent sessions handling by the linux NFS client, and i would like
to understand a few things about the linux NFS client - i read all
relevant material on www.linux-nfs.org, and spent a while reading the
relevant recovery code in the nfs4.1 client kernel sources, but i am
missing some things (a pointer to the relevant part in the recovery code
will be appreciated as well):
1. suppose there is a persistent session that got disconnected (because
of a server restart, for example). i see that the client is re-sending
all the in-flight commands as part of
the recovery. however, suppose that one of the commands was a
compound command containing 2 requests, and the reply to the first of
them was NFS4_OK, and to the 2nd it was NFS4ERR_DELAY - will the
client's code know that after it finishes recovery of the session - then
when it creates a new session, it needs to re-send the 2nd request in
this compound command? the broader question is about a compound with N
commands, where the first X have an NFS4_OK reply and the last N-X have
NFS4_DELAY - will the client re-send a new compound with the last N-X
commands after establishing a new session?
2. if there is a non-persistent session, on which the client sent a
non-idempotent request (e.g. rename of a file into a different
directory), and the server restarted before the client received the
response - will the client just blindly re-send the same request again
after establishing a new session, or will it take some measures to
attempt to understand whether the command was already executed? i.e. if
the server already executed the rename, then re-sending it will return a
failure to locate the source file handle (because it moved to a new
directory). does the linux NFS client attempt to recover from this, or
will it simply return an error to the application layer?
3. what NFS server with persistent sessions is used (or was used) when
testing the persistent sessions support in the linux NFS client? the
linux NFS server, as far as i understood, cannot support persistent
sessions (due to lack of assured persistent memory).
thanks in advance,
--guy keren
Vast data.
