[LU-7015] Grant space and reserved blocks percent parameters

• Type: Question/Request
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.8.0
• Affects Version/s: Lustre 2.5.4
• Environment: RHEL-6.6, lustre-2.5.4
• Assignee: Oleg Drokin
• Reporter: Jesse Hanley

Description

Our system space utilization on one of our systems is high, and as we work to prune some of this data, we're exploring some other space tunings.

One of our admins noted the "cur_grant_bytes" osc parameter. When we looked at a few clients, we saw that this variable often exceeds the max_dirty_mb, sometimes by an order of magnitude. We usually use 64MB of dirty cache per osc per client. Is there an upper limit to this cur_grants_bytes parameter? What are the side effects of setting this value to some lower value (or 0)? Can we reduce this client grant while there is active I/O, and can we do this for all osc connections simultaneously (for a collective of millions of osc connections) for a system? Is this documented well anywhere?

Additionally, we are looking into tuning the reserved_blocks_percent parameter. The Lustre manual states that 5% is the minimum, but is that a sane value for all OST sizes?

Thanks,
–
Jesse

Issue Links

• is related to: LU-3859 grant shrinker floods OST and produce a large load