[LUDOC-317] document OST reserved space tunables

• Type: New Feature
• Resolution: Fixed
• Priority: Minor
• Assignee: Lustre Manual Triage
• Reporter: Andreas Dilger

Description

Document the new OST free space tunables from http://review.whamcloud.com/15731 "LU-6910: osp: add procfs values for OST reserved size" in the user manual.

osp_pre_status=-ENOSPC is used to skip OST from object allocation.
The error was set when OST available space is less than 0.1% of total
OST size. This value is not configurable, so procfs files was
added:
reserved_mb_low - low watermark, if available space is less
		  than it, object allocation is stopped.
reserved_mb_high - highw watermark, if available space is more
		   than it, object allocation is enabled.

By default ~0.1% is reserved as low watermark. The high watermark
is twice bigger than the low by default.
High and low watermark could be changed by:
lctl set_param osp.lustre-OST0000-osc-MDT0000.reserved_mb_high=1024

When object allocation is disabled, a clients could appened to
existing files. And 0.1% is too low for them. For example, OST size
is 8TB, 0.1% is 8GB, if cluster has 1k clients, reserved space is
~8MB per client. The main reason of the patch is ability to increase
reserved space.

Issue Links

• is blocking: LU-6910 Configurable values for OST reserved size

Comments

[Gerrit Updater]

Andreas Dilger ([e-mail]) merged in patch http://review.whamcloud.com/17560/
Subject: LUDOC-317 proc: OST reserved size
Project: doc/manual
Branch: master
Current Patch Set:
Commit: 862043c93966841745c57818fcf40bd86e31902e

[Gerrit Updater]

Alexander Boyko ([e-mail]) uploaded a new patch: http://review.whamcloud.com/17560
Subject: LUDOC-317 proc: OST reserved size
Project: doc/manual
Branch: master
Current Patch Set: 1
Commit: cddc05720f42a77ee6a3c045dd53f9fbd1a956a6

[Andreas Dilger]

For details on how to submit changes to the manual, please see:

• https://wiki.hpdd.intel.com/display/PUB/Making+changes+to+the+Lustre+Manual
• https://wiki.hpdd.intel.com/display/PUB/Code+Documentation+Guidelines