[LU-3660] Can't disable ACL support with ZFS MDT

• Type: Bug
• Resolution: Fixed
• Priority: Critical
• Fix Version/s: Lustre 2.7.0, Lustre 2.5.4
• Affects Version/s: Lustre 2.4.0
• Labels: llnl prz zfs
• Severity: 3
• Assignee: Lai Siyao
• Reporter: Ned Bass (Inactive)

Description

With ldiskfs, the MDT can be mounted with -o noacl to disable POSIX ACL support. With ZFS, that option seems to have no effect, and clients are still able to set and honor ACLs. It would be desirable to be able to turn off ACLs, as they can be detrimental to performance. For example, the cp -a command tries to write the xattr system.posix_acl_access on every destination file, regardless of whether the source file has that attribute. The ACL update is handled synchronously on the MDT, so the request handler has to wait for a ZFS transaction group to sync. This can introduce significant latency on a busy MDS, effectively limiting the per-file copy rate to the txg sync rate. On ldiskfs, cp -a performance is significantly improved by disabling ACLs.

(This performance problem is a separate issue that may be helped by integrating ZIL support in Lustre. Turning off ACLs is a temporary workaround.)

LLNL-bug-ID: TOSS-2207

Issue Links

• is related to: LU-3671 why are permission changes synchronous?