Date: Thu, 18 Feb 2016 15:53:10 -0500 From: Mike Tancsa <mike@sentex.net> To: Paul Macdonald <paul@ifdnrg.com>, freebsd-questions@freebsd.org Subject: Re: ZFS + dovecot Message-ID: <56C62F36.4050606@sentex.net> In-Reply-To: <56C62724.60201@ifdnrg.com> References: <56C62724.60201@ifdnrg.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 2/18/2016 3:18 PM, Paul Macdonald wrote:
> I'm starting to see reduced performance on a 2 disk SATA server with a
> mirrored 2TB pool running dovecot.
More memory helps with ZFS of course. How fragmented is your spool ?
Its generally a bad thing for performance once things get above 80%
capacity. Is free space greater than 20% ?
Also, If you do
zpool get fragmentation <pool name>
How high is the fragmentation ?
How upto date is your OS ? Sometimes I find with certain workloads,
setting the limit of arc is better for performance on low memory
servers. I had a box (12G of RAM) that does squid which needed
vfs.zfs.arc_max set in /boot/loader.conf so that arc would not take too
much memory. But other boxes never needed that. Not sure when it
becomes an issue and needs manual intervention. But might be something
to look at.
On our imap/pop3 server, (32G, 16G ARC limit), ARC works well
------------------------------------------------------------------------
ZFS Subsystem Report Thu Feb 18 15:50:30 2016
------------------------------------------------------------------------
ARC Efficiency: 243.15m
Cache Hit Ratio: 90.12% 219.11m
Cache Miss Ratio: 9.88% 24.03m
Actual Hit Ratio: 88.46% 215.08m
Data Demand Efficiency: 95.49% 85.08m
Data Prefetch Efficiency: 5.52% 4.81m
CACHE HITS BY CACHE LIST:
Anonymously Used: 0.03% 59.64k
Most Recently Used: 8.51% 18.64m
Most Frequently Used: 89.66% 196.44m
Most Recently Used Ghost: 0.47% 1.03m
Most Frequently Used Ghost: 1.34% 2.94m
CACHE HITS BY DATA TYPE:
Demand Data: 37.08% 81.25m
Prefetch Data: 0.12% 265.88k
Demand Metadata: 60.96% 133.57m
Prefetch Metadata: 1.84% 4.03m
CACHE MISSES BY DATA TYPE:
Demand Data: 15.96% 3.83m
Prefetch Data: 18.92% 4.55m
Demand Metadata: 58.73% 14.12m
Prefetch Metadata: 6.39% 1.54m
------------------------------------------------------------------------
L2 SSD is hardly touched
------------------------------------------------------------------------
ZFS Subsystem Report Thu Feb 18 15:50:57 2016
------------------------------------------------------------------------
L2 ARC Summary: (HEALTHY)
Passed Headroom: 1.94m
Tried Lock Failures: 84.50k
IO In Progress: 109
Low Memory Aborts: 1
Free on Write: 1.29k
Writes While Full: 611
R/W Clashes: 0
Bad Checksums: 0
IO Errors: 0
SPA Mismatch: 566.26m
L2 ARC Size: (Adaptive) 16.23 GiB
Header Size: 0.04% 6.77 MiB
L2 ARC Breakdown: 24.03m
Hit Ratio: 4.71% 1.13m
Miss Ratio: 95.29% 22.90m
Feeds: 592.45k
L2 ARC Buffer:
Bytes Scanned: 41.86 TiB
Buffer Iterations: 592.45k
List Iterations: 2.37m
NULL List Iterations: 85.88k
L2 ARC Writes:
Writes Sent: (FAULTED) 128.62k
Done Ratio: 100.00% 128.62k
Error Ratio: 0.00% 0
------------------------------------------------------------------------
---Mike
--
-------------------
Mike Tancsa, tel +1 519 651 3400
Sentex Communications, mike@sentex.net
Providing Internet services since 1994 www.sentex.net
Cambridge, Ontario Canada http://www.tancsa.com/
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?56C62F36.4050606>