Lustre 1.6 Operations Manual

20.2 Lustre I/O Tunables
The section describes I/O tunables.
/proc/fs/lustre/llite/-/max_cache_mb
# cat /proc/fs/lustre/llite/lustre-ce63ca00/max_cached_mb 128
This tunable is the maximum amount of inactive data cached by the client (default is
3/4 of RAM).
20.2.1 Client I/O RPC Stream Tunables
The Lustre engine always attempts to pack an optimal amount of data into each I/O
RPC and attempts to keep a consistent number of issued RPCs in progress at a time.
Lustre exposes several tuning variables to adjust behavior according to network
conditions and cluster size. Each OSC has its own tree of these tunables. For
example:
$ ls -d /proc/fs/lustre/osc/OSC_client_ost1_MNT_client_2 /localhost
/proc/fs/lustre/osc/OSC_uml0_ost1_MNT_localhost
/proc/fs/lustre/osc/OSC_uml0_ost2_MNT_localhost
/proc/fs/lustre/osc/OSC_uml0_ost3_MNT_localhost
$ ls /proc/fs/lustre/osc/OSC_uml0_ost1_MNT_localhost
blocksizefilesfreemax_dirty_mb ost_server_uuid stats
... and so on.
RPC stream tunables are described below.
/proc/fs/lustre/osc//max_dirty_mb
This tunable controls how many MBs of dirty data can be written and queued up in
the OSC. POSIX file writes that are cached contribute to this count. When the limit is
reached, additional writes stall until previously-cached writes are written to the
server. This may be changed by writing a single ASCII integer to the file. Only
values between 0 and 512 are allowable. If 0 is given, no writes are cached.
Performance suffers noticeably unless you use large writes (1 MB or more).
/proc/fs/lustre/osc//cur_dirty_bytes
This tunable is a read-only value that returns the current amount of bytes written
and cached on this OSC.
20-12 Lustre 1.6 Operations Manual • September 2008