[LU-16479] Automatically manage/control DEGRADED ZFS OST's

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Affects Version/s: Upstream, Lustre 2.15.0
• Environment: Lustre filesystem with ZFS as backend filesystem for OST's.

Epic/Theme

zfs

Epic

server zfs

• Assignee: Akash B
• Reporter: Akash B

Description

We have the obdfilter.testfs-OST000*.degraded value set/unset by zedlets (/etc/zfs/zed.d/statechange-lustre.sh) based on zpool being DEGRADED/ONLINE, We'd like to have this behavior enabled/disabled through an option so that we have I/O or newer allocations to DEGRADED OST's as well and hence there is no degradation in net bandwidth of the filesystem due to the degraded OSTs.
 
Introduce a new Lustre-specific ZFS dataset user property (lustre:autodegrade=on|off) for this purpose. Update the Lustre zedlet and also extend the mkfs.lustre utility to add this property by default when creating a new Lustre server(only for ZFS OSTs). The default behavior would remain the same (lustre:autodegrade=on) which disables new allocations to DEGRADED OSTs.
Creating a user property has a few advantages:

1. User properties are a generic ZFS feature and won't be interpreted by ZFS itself. No ZFS changes are needed.
2. The property can be set per dataset providing more granularity.
3. The property is persistent and will survive reboots.