On Feb 17, 2010, at 7:54 AM, Mark Heily wrote: > 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?
No. c is the target size, not the actual size. > Or are there legitimate cases when the ARC cache will shrink below the c_min > limit. At boot, for instance. -- richard > > 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 > > _______________________________________________ > zfs-code mailing list > zfs-code at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-code ZFS storage and performance consulting at http://www.RichardElling.com ZFS training on deduplication, NexentaStor, and NAS performance http://nexenta-atlanta.eventbrite.com (March 15-17, 2010)
