@@ -64,6 +64,92 @@ fio for 20 secs with directio, qd of 8, 1 libaio thread:
128K read: IOPS=24.4k, BW=3050MiB/s (3198MB/s)(59.6GiB/20001msec)
128K write: IOPS=11.4k, BW=1430MiB/s (1500MB/s)(27.9GiB/20001msec)
+FAQ
+===
+
+1. What are the use cases for LOCALIO?
+
+ a. Workloads where the NFS client and server are on the same host
+ realize improved IO performance. In particular, it is common when
+ running containerised workloads for jobs to find themselves
+ running on the same host as the knfsd server being used for
+ storage.
+
+2. What are the requirements for LOCALIO?
+
+ a. Bypass use of the network RPC protocol as much as possible. This
+ includes bypassing XDR and RPC for open, read, write and commit
+ operations.
+ b. Allow client and server to autonomously discover if they are
+ running local to each other without making any assumptions about
+ the local network topology.
+ c. Support the use of containers by being compatible with relevant
+ namespaces (e.g. network, user, mount).
+ d. Support all versions of NFS. NFSv3 is of particular importance
+ because it has wide enterprise usage and pNFS flexfiles makes use
+ of it for the data path.
+
+3. Why doesn’t LOCALIO just compare IP addresses or hostnames when
+ deciding if the NFS client and server are co-located on the same
+ host?
+
+ Since one of the main use cases is containerised workloads, we cannot
+ assume that IP addresses will be shared between the client and
+ server. This sets up a requirement for a handshake protocol that
+ needs to go over the same connection as the NFS traffic in order to
+ identify that the client and the server really are running on the
+ same host. The handshake uses a secret that is sent over the wire,
+ and can be verified by both parties by comparing with a value stored
+ in shared kernel memory if they are truly co-located.
+
+4. Does LOCALIO improve pNFS flexfiles?
+
+ Yes, LOCALIO complements pNFS flexfiles by allowing it to take
+ advantage of NFS client and server locality. Policy that initiates
+ client IO as closely to the server where the data is stored naturally
+ benefits from the data path optimization LOCALIO provides.
+
+5. Why not develop a new pNFS layout to enable LOCALIO?
+
+ A new pNFS layout could be developed, but doing so would put the
+ onus on the server to somehow discover that the client is co-located
+ when deciding to hand out the layout.
+ There is value in a simpler approach (as provided by LOCALIO) that
+ allows the NFS client to negotiate and leverage locality without
+ requiring more elaborate modeling and discovery of such locality in a
+ more centralized manner.
+
+6. Why is having the client perform a server-side file OPEN, without
+ using RPC, beneficial? Is the benefit pNFS specific?
+
+ Avoiding the use of XDR and RPC for file opens is beneficial to
+ performance regardless of whether pNFS is used. Especially when
+ dealing with small files its best to avoid going over the wire
+ whenever possible, otherwise it could reduce or even negate the
+ benefits of avoiding the wire for doing the small file I/O itself.
+ Given LOCALIO's requirements the current approach of having the
+ client perform a server-side file open, without using RPC, is ideal.
+ If in the future requirements change then we can adapt accordingly.
+
+7. Why is LOCALIO only supported with UNIX Authentication (AUTH_UNIX)?
+
+ Strong authentication is usually tied to the connection itself. It
+ works by establishing a context that is cached by the server, and
+ that acts as the key for discovering the authorisation token, which
+ can then be passed to rpc.mountd to complete the authentication
+ process. On the other hand, in the case of AUTH_UNIX, the credential
+ that was passed over the wire is used directly as the key in the
+ upcall to rpc.mountd. This simplifies the authentication process, and
+ so makes AUTH_UNIX easier to support.
+
+8. How do export options that translate RPC user IDs behave for LOCALIO
+ operations (eg. root_squash, all_squash)?
+
+ Export options that translate user IDs are managed by nfsd_setuser()
+ which is called by nfsd_setuser_and_check_port() which is called by
+ __fh_verify(). So they get handled exactly the same way for LOCALIO
+ as they do for non-LOCALIO.
+
RPC
===