I have noticed a strange issue on two idle Solaris 10 U6 systems where the reported size of the ARC cache is less than c_min. I was under the impression that c_min is a hard limit on the minimum size of the ARC cache [1]. As an example, I have included the output of arc_summary[2] and kstat[3] for one of the systems.
Is the formula "arcstats:size >= arcstats:c_min" always true? Or are there legitimate cases when the ARC cache will shrink below the c_min limit. Thanks, - Mark [1] http://mail.opensolaris.org/pipermail/perf-discuss/2009-June/002312.html [1] Excerpt from Ben Rockwood's arc_summary: System Memory: Physical RAM: 32046 MB Free Memory : 4255 MB LotsFree: 496 MB ZFS Tunables (/etc/system): ARC Size: Current Size: 288 MB (arcsize) Target Size (Adaptive): 25728 MB (c) Min Size (Hard Limit): 3877 MB (zfs_arc_min) Max Size (Hard Limit): 31022 MB (zfs_arc_max) [2] Output of "kstat zfs:0:arcstats" module: zfs instance: 0 name: arcstats class: misc c 26978509172 c_max 32529489920 c_min 4066186240 crtime 2251383.06747617 data_size 166427648 deleted 20710 demand_data_hits 1708848 demand_data_misses 161416 demand_metadata_hits 2532283 demand_metadata_misses 129957 evict_skip 455 hash_chain_max 7 hash_chains 66762 hash_collisions 221681 hash_elements 323508 hash_elements_max 330316 hdr_size 67452840 hits 4582847 l2_abort_lowmem 0 l2_cksum_bad 0 l2_evict_lock_retry 0 l2_evict_reading 0 l2_feeds 0 l2_free_on_write 0 l2_hdr_size 0 l2_hits 0 l2_io_error 0 l2_misses 0 l2_read_bytes 0 l2_rw_clash 0 l2_size 0 l2_write_bytes 0 l2_writes_done 0 l2_writes_error 0 l2_writes_hdr_miss 0 l2_writes_sent 0 memory_throttle_count 0 mfu_ghost_hits 630167 mfu_hits 3166923 misses 1090660 mru_ghost_hits 137293 mru_hits 1076653 mutex_miss 2290 other_size 69767200 p 3228355146 prefetch_data_hits 5940 prefetch_data_misses 761634 prefetch_metadata_hits 335776 prefetch_metadata_misses 37653 recycle_miss 3549 size 303647688 snaptime 3616598.76049297
