* Mike Snitzer <[email protected]> wrote:
> On Thu, Jul 14 2016 at 12:21am -0400,
> Jon Bernard <[email protected]> wrote:
>
> > Do you have any intuition on where to start looking?
>
> Joe asked me a very basic/obvious question: is block zeroing enabled?
> (block zeroing is enabled by default -- you have to know to disable it)
Ah, I failed to mention that I did read about that in the manpage and
disabled it. Just to be sure, here is my lvs output:
# lvs -o +zero
LV VG Attr LSize Pool Origin Data% Meta% Move Log
Cpy%Sync Convert Zero
pool1 thin twi-aot--- 1.00t 9.77 0.35
pool2 thin twi-aot--- 1.00t 0.00 0.03
thick thin -wi-a----- 100.00g
unknown
thindisk1 thin Vwi-a-t--- 100.00g pool1 100.00
unknown
I believe we'd see a 'z' in attr field if it were enabled.
> If zeroing wasn't disabled that could explain some of the sizable
> performance differences. Please use/test the 'skip_block_zeroing'
> feature if you aren't already (also see the "Zeroing' section of the
> 'lvmthin' manpage).
If my understanding is correct, even with zeroing enabled, my initial
sequential write that that caused the volume to become fully allocated
would have alleviated any further zeroing during the random write test.
--
Jon
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