[Trac-bugs] [PC-BSD Trac] #704: ZFS and heavy resource utilization

PC-BSD trac at pcbsd.org
Sun Feb 17 22:41:21 PST 2013

#704: ZFS and heavy resource utilization
 Reporter:  friedg   |       Type:  System Enhancement
   Status:  new      |   Priority:  major
Milestone:           |  Component:  System Configuration
  Version:  9.1-RC3  |   Keywords:  zfs, ufs
 PCBSD with zfs has high resource (processing and memory) utilization and
 has been the target of multiple user complaints on web forums.  The canned
 answer is usually with regard to kernel memory allocation (mem_wire,
 mem_active, mem_inactive, and mem_cache) for optimal performance and that
 unused memory is wasted memory.

 The complaint is not due to kernel maximizing memory allocation, it's with
 respect to mem_active memory being considerably higher than if a ufs or a
 Linux ext3 or 4 file system were being used.  ZFS has an inherently higher
 mem_active memory utilization due to the arc algorithm and sha256 checksum
 operations on hard drive reads.  Increasing the zfs cache puts a higher
 load on mem_active and decreasing zfs cache puts a higher load on the
 processor, even at idle.  This may lead to a certain level of
 dissatisfaction with regard to system performance and give PCBSD a poor
 reputation.  I've noticed 100mb of mem_active being used on a headless
 PCBSD/zfs installation, which is far higher than a normal 20mb with ufs.
 I've also witnessed 50% processor utilization when the system is idle with
 a core2quad processor.

 The proponents of zfs stipulate the data integrity advantage it has with
 respect to ufs, ext4, and fat32.  However, the end user may not recognize
 this, especially with poor performance.  A compromise could be if the
 default pcbsd installation utilized ufs for system partitions and zfs for
 user data (/usr and /home).

Ticket URL: <http://trac.pcbsd.org/ticket/704>
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