latency: avoid mixing HFS Plus and ZFS on a single hard disk

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latency: avoid mixing HFS Plus and ZFS on a single hard disk

Post by grahamperrin » Fri Nov 09, 2012 12:59 am

dbrady wrote:… It's recommended that in most cases you should not share a disk with ZFS and another file system -- particularly with HFS+. Since HFS+ has a single global lock for all metadata updates (held across the I/O) it is highly sensitive to disk latencies. So for a typical HDD you won't want to share a disk. In the case of your Air with an SSD, you could share with less performance impact than an HDD. If file system performance is less of an issue for you, the ''zpool create'' command will let you use a partition (e.g. /dev/disk2s3) even tough we recommend passing a whole disk slice (e.g. /dev/disk2).


One phrase caught my eye:

Since HFS+ has a single global lock for all metadata updates (held across the I/O) it is highly sensitive to disk latencies

For further information I was referred to What's wrong with HFS+ on page twelve of nineteen of Mac OS X 10.7 Lion: the Ars Technica review | Ars Technica (2011-07-20).
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cross reference

Post by grahamperrin » Mon Nov 12, 2012 2:54 am

At https://groups.google.com/d/msg/zfs-mac ... 2BCm-uss4J

Daniel Becker wrote:Note that this refers to performance degradation on the HFS+ side, not on the ZFS side.
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mixing HFS Plus and ZFS in a MacBook Pro with Retina display

Post by grahamperrin » Sun Apr 14, 2013 8:02 am

At viewtopic.php?p=4624#p4624

jollyjinx wrote:… A ZFS home does not feel fast compared to HFS+ … 15" MBPr with a flash drive …


I guess that in that laptop, the one solid-state drive is used for both HFS Plus (including a home directory) and ZFS (for a home directory for a different user).

>> less performance impact than an HDD

… but still, some negative impact.
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