[LU-19573] Reduce default max_dirty_mb for MDC

• Type: Improvement
• Resolution: Unresolved
• Priority: Medium
• Affects Version/s: Lustre 2.17.0
• Labels: easy
• Severity: 3
• Assignee: WC Triage
• Reporter: Andreas Dilger

Description

The default max_dirty_mb value for both OSC and MDC devices is 2000 MiB, but for most MDTs without DoM it does not make sense to allow so much cached data, because there is relatively little space available, the maximum file size is usually 1 MiB, and this consumes all of the grant for the target and causes false ENOSPC errors.

It would be better to reduce the default value for MDCs to a smaller value, maybe 64 or 128 MiB. Possibly this can be based on the average free space on the MDT.

Issue Links

• is related to: LU-19262 grant shrink should be done more quickly when filesystem becomes full