zfs

[Peter Jeremy]

On 2015-Mar-13 23:45:10 -0400, Brett Wynkoop <freebsd-arm at wynn.com> wrote:
>While I think there would be a further space savings with dedupe I did
>not want the system bogged down doing that work.  The BeagleBone is
>after all a pretty small system.

Whilst an all-flash pool removes one of the main killers for dedupe, I
suspect that the extra RAM to handle the DDT would outweigh the
possible space-savings.

>vfs.zfs.arc_max="24M"
...
>With the above arc I am getting about 50% arc cache hits:

Depending on your workload, you might find that increasing
vfs.zfs.arc_meta_limit might help overall performance - at least on
my x86 server, I find the default (25% of arc_max) a bit small.

>I wonder if we could do zfs on root.....hmmmm.

You'd need to build your own ubldr but it should be doable.

>fast and without crashing the system.  I also get the advantage of a
>compressed filesystem and in addition to allowing me more storage it
>may account for the better write performance.  There are fewer bits to
>write, so the slowness of flash media is somewhat compensated for.

ZFS compression trades CPU resources for IO performance.  For a modern
x86 system, it's virtually always a win but the BBB has far less CPU
available (though the flash is also very slow).

>> Since zfs checksums everything you may well just be seeing it
>> detecting corruption and repairing it.
>
>You could be right on this one.  I think I need to dig out my other
>Beagle Bone and shift the sd and usb flash over to it and run the
>series of tests against ufs again on the new hardware.  I say new
>because I have never fired up the other BBone.

Note that ZFS can't repair things unless you have redundant copies.
Whilst there are redundant copies of metadata by default, there is
only one copy of data - which is why you have:
>errors: Permanent errors have been detected in the following files:
>
>        /export/src/contrib/llvm/tools/clang/lib/Sema/SemaExpr.cpp
>        /export/ports/packages/All/perl5-5.18.4_11.txz
>        /export/ports/distfiles/rsync-3.1.1.tar.gz
>        /export/ports/distfiles/readline-6.3.tar.gz
>        /export/ports/comms/wsjt/files/configure

You might like to set copies=2 if you don't have redundancy at the pool level.

>        bbexport/ports:<0x253db>

This is probably a lost metadata block.

-- 
Peter Jeremy
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