Date: Tue, 4 Aug 2015 22:12:59 +0100 From: Mark Blackman <mark@exonetric.com> To: javocado <javocado@gmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: pw operations slow under zfs load Message-ID: <A63EA6D5-F7D5-4726-8108-7530061CA255@exonetric.com> In-Reply-To: <CAP1HOmSuohyh=mUQ=BChrsuysPQK=v3hdPAays-zn-zadZUKjA@mail.gmail.com> References: <CAP1HOmSuohyh=mUQ=BChrsuysPQK=v3hdPAays-zn-zadZUKjA@mail.gmail.com>
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> On 4 Aug 2015, at 22:07, javocado <javocado@gmail.com> wrote:
>=20
> Hi,
>=20
> We have a pretty busy ZFS pool running on an 8.3 AMD system. We are
> noticing that when the pool is busy pw-related operations seem to =
take a
> long time to complete:
>=20
> # time pw unlock 1000
> 0.007u 0.036s 0:39.72 0.0% 45+1953k 0+113io 0pf+0w
>=20
> # time pw lock 1000
> 0.032u 0.022s 1:09.63 0.0% 24+1132k 0+114io 0pf+0w
>=20
> Wile the command is running, we note that the process is locked in the =
D
> state:
>=20
> root 85051 0.0 0.0 5832 960 0 D+ 1:53PM 0:00.02
> /usr/sbin/pwd_mkdb -u 1000 /etc/master.passwd
>=20
> We also note that there is next to 0 disk activity on the boot volume:
>=20
> # gstat -f ad
>=20
> dT: 1.005s w: 1.000s filter: ad
> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
> 0 0 0 0 0.0 0 0 0.0 0.0| ad6
> 0 0 0 0 0.0 0 0 0.0 0.0| ad8
> 0 0 0 0 0.0 0 0 0.0 0.0| ad10
> 0 0 0 0 0.0 0 0 0.0 0.0| ad12
>=20
> And plenty of free mem:
>=20
> Mem: 400M Active, 3391M Inact, 128G Wired, 1935M Cache, 14G Buf, 6055M =
Free
>=20
> So, what's going on here? How does a busy pool with it's own set of =
drives
> (which operate off an HBA) affect the speed of operations involving =
the
> boot volume (a UFS-formatted SSD connected to the mobo)?
Maybe some ktrace operations are in order? I remember, about 15 years =
ago, discovering that that =E2=80=98-s=E2=80=99 option can make a big =
difference.
-s cachesize
Specify in megabytes the size of the memory cache used by the =
hash-
ing library. On systems with a large user base, a small =
cache size
can lead to prohibitively long database file rebuild times. =
As a
rough guide, the memory usage of pwd_mkdb in megabytes will =
be a
little bit more than twice the figure specified here. The =
default
is 2 megabytes.
- Mark
=20
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