Re: ZFS L2ARC - incorrect size and abnormal system load on r255173

On 2013-10-10 05:22, Vitalij Satanivskij wrote:
> Same situation hapend yesterday again :( 
>
> What's confuse me while trying to understend where I'm wrong
>
>
> Firt some info.
>
> We have zfs pool  "POOL" and one more zfs on it "POOL/zfs"
>
> POOL - have only primarycache enabled "ALL" 
> POOL/zfs - have both primay and secondary for "ALL"
>
> POOL have compression=lz4
>
> POOL/zfs have none
>
>
> POOL - have around 9TB data
>
> POOL/zfs - have 1TB
>
> Secondary cache have configuration - 
>
>         cache
>           gpt/cache0    ONLINE       0     0     0
>           gpt/cache1    ONLINE       0     0     0
>           gpt/cache2    ONLINE       0     0     0
>
> gpt/cache0-2 it's intel sdd SSDSC2BW180A4 180gb 
>
> So full real size  for l2 is 540GB (realy 489gb)
>
> First question  - data on l2arc will be compressed on not?
>
> Second in stats we see 
>
> L2 ARC Size: (Adaptive)                         2.08    TiB
>
> eary it was 1.1 1.4 ...
>
> So a) how cache can be biger than zfs it self
>    b) in case it's not compressed (answer for first question) how it an be biger than real ssd size?
>
>
> one more coment if l2 arc size grove above phisical sizes I se  next stats 
>
> kstat.zfs.misc.arcstats.l2_cksum_bad: 50907344
> kstat.zfs.misc.arcstats.l2_io_error: 4547377
>
> and growing.
>
>
> System is r255173 with patch from rr255173
>
>
> At last maybe somebody have any ideas what's realy hapend...
>
>
>
>
>
> Vitalij Satanivskij wrote:
> VS> 
> VS> One more question - 
> VS> 
> VS> we have two counter - 
> VS> 
> VS> kstat.zfs.misc.arcstats.l2_size: 1256609410560
> VS> kstat.zfs.misc.arcstats.l2_asize: 1149007667712
> VS> 
> VS> can anybody explain how to understand them i.e.  l2_asize - real used space on l2arc an l2_size - uncompressed size,
> VS> 
> VS> or maybe something else ?
> VS> 
> VS> 
> VS> 
> VS> Vitalij Satanivskij wrote:
> VS> VS> 
> VS> VS> Data on pool have compressratio around 1.4 
> VS> VS> 
> VS> VS> On diferent servers with same data type and load L2 ARC Size: (Adaptive) can be diferent 
> VS> VS> 
> VS> VS> for example 1.04    TiB vs  1.45    TiB
> VS> VS> 
> VS> VS> But it's all have same porblem  - grow in time.
> VS> VS> 
> VS> VS> 
> VS> VS> More stange for us - 
> VS> VS> 
> VS> VS> ARC: 80G Total, 4412M MFU, 5040M MRU, 76M Anon, 78G Header, 2195M Other
> VS> VS> 
> VS> VS> 78G header size and ubnormal - 
> VS> VS> 
> VS> VS> kstat.zfs.misc.arcstats.l2_cksum_bad: 210920592
> VS> VS> kstat.zfs.misc.arcstats.l2_io_error: 7362414
> VS> VS> 
> VS> VS> sysctl's growing avery second.
> VS> VS> 
> VS> VS> All part's of server (as hardware part's) in in normal state.
> VS> VS> 
> VS> VS> After reboot no problem's for some period untile cache size grow to some limit.
> VS> VS> 
> VS> VS> 
> VS> VS> 
> VS> VS> Mark Felder wrote:
> VS> VS> MF> On Mon, Oct 7, 2013, at 13:09, Dmitriy Makarov wrote:
> VS> VS> MF> > 
> VS> VS> MF> > How can L2 ARC Size: (Adaptive) be 1.44 TiB (up) with total physical size
> VS> VS> MF> > of L2ARC devices 490GB?
> VS> VS> MF> > 
> VS> VS> MF> 
> VS> VS> MF> http://svnweb.freebsd.org/base?view=revision&revision=251478
> VS> VS> MF> 
> VS> VS> MF> L2ARC compression perhaps?
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Some background on L2ARC compression for you:

http://wiki.illumos.org/display/illumos/L2ARC+Compression

http://svnweb.freebsd.org/base?view=revision&revision=251478

Are you sure that compression on pool/zfs is off? it would normally
inherit from the parent, so double check with: zfs get compression pool/zfs

Is the data on pool/zfs related to the data on the root pool? if
pool/zfs were a clone, and the data is actually used in both places, the
newer 'single copy ARC' feature may come in to play:
https://www.illumos.org/issues/3145




-- 
Allan Jude