[TUHS] ZFS (was: Re: MacOS X is Unix (tm))

Michael Kjörling michael at kjorling.se
Wed Jan 4 01:52:52 AEST 2017

On 3 Jan 2017 14:17 +0100, from schily at schily.net (Joerg Schilling):
> BTW: ZFS has a similar problem as Linux: It is extremely slow when you ask it 
> to to things in a way that result in a known state. ZFS however does not result 
> in a rotten FS when you switch the system off while it is updating the FS.

In all fairness to it, ZFS never (at least that I have seen) _claims_
to be a high performance file system. Lots of people (myself included)
point out that it is _anything but_. Its Merkle tree data structures
on disk, copy-on-write behavior and ubiquitous, nearly free snapshots
are, in fact, prone to encourage fragmentation along with causing
normal I/O patterns to require massive seeking on rotational media.
Its saving grace in terms of performance is caching; just try setting
primarycache=none or sync=always and observe your system grind to a
halt I/O-wise almost no matter what else you do.

Yes, I use ZFS; nearly exclusively so on my main machine. Yes, it has
saved my rear a few times with disk/cabling/controller combinations
that have somehow not been quite happy together (for whatever reason,
LSI 9211, SFF-8087 to SFF-8482 breakout cables, and HGST SATA disks is
not a good combination). But not even ZFS is perfect, and its design
does have several sharp edges to watch out for alongside the
performance implications. Where ZFS shines IMO is in the end-to-end
integrity guarantees department and its integration of the volume and
file system managers into a cohesive whole.

Michael Kjörling • https://michael.kjorling.semichael at kjorling.se
                 “People who think they know everything really annoy
                 those of us who know we don’t.” (Bjarne Stroustrup)

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