ARC "pressured out", how to control/stabilize ? (reformatted to text/plain)

[Andriy Gapon]

on 11/02/2014 16:38 Vitalij Satanivskij said the following:
> Get first result's while testing l2 without compression 
> 
> Memory leak is not seen for now ( system working only 20 hours) but 
> zfs stats saying that l2 degraded 
> 
> output of zfs-stats -L: 
> 
> ------------------------------------------------------------------------
> ZFS Subsystem Report                            Tue Feb 11 16:34:43 2014
> ------------------------------------------------------------------------
> 
> L2 ARC Summary: (DEGRADED)
>         Passed Headroom:                        3.81m
>         Tried Lock Failures:                    79.52m
>         IO In Progress:                         9
>         Low Memory Aborts:                      235
>         Free on Write:                          54.37k
>         Writes While Full:                      9.68k
>         R/W Clashes:                            2.82k
>         Bad Checksums:                          211.94k
>         IO Errors:                              0
>         SPA Mismatch:                           58.33m
> 
> L2 ARC Size: (Adaptive)                         243.32  GiB
>         Header Size:                    0.36%   895.11  MiB
> 
> L2 ARC Evicts:
>         Lock Retries:                           45
>         Upon Reading:                           0
> 
> L2 ARC Breakdown:                               38.15m
>         Hit Ratio:                      17.79%  6.79m
>         Miss Ratio:                     82.21%  31.36m
>         Feeds:                                  88.88k
> 
> L2 ARC Buffer:
>         Bytes Scanned:                          292.58  TiB
>         Buffer Iterations:                      88.88k
>         List Iterations:                        5.63m
>         NULL List Iterations:                   17.26k
> 
> L2 ARC Writes:
>         Writes Sent: (FAULTED)                          77.95k
>           Done Ratio:                   100.00% 77.95k
>           Error Ratio:                  0.00%   0
> 
> ------------------------------------------------------------------------
> 
> As you can see we have Bad Checksums:                          211.94k and growing 
> 
> and also 
>         Writes Sent: (FAULTED)                          77.95k
>           Done Ratio:                   100.00% 77.95k

I have no clue how this tool summarizes the statistics.  I think that I would
prefer output of vfs.zfs and kstat sysctl hierarchies.

I have no idea what could cause those checksum errors.  This will have to be
investigated separately when I (or someone else) have time.

> 
> Another question: Please provide revision number of arc.c against which was diff created (http://people.freebsd.org/~avg/l2arc-b_tmp_cdata-diag.2.patch)
> Because in version in head have some small diferent's and I need manualy aply patch.

I've just updated the patch in-place.  It is now based r261726.
Sorry for the previous version which was against my local tree.

-- 
Andriy Gapon