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Re: maximum LUN [message #64002 is a reply to message #63928]

Tue, 25 November 2008 02:55

greg.addr
Messages: 160
Registered: May 2007

Senior Member

I made some tests with data reads at different separations to see how
opening/closing affects the caching. The effect's not large, but
appears to favour files held open.

Still, if we agree the cost of opening a file is very low, I don't see
why the number open needs to be rationed so strictly.

pro filetest
f1="D:\mydocs\data\hrsc\lev4\2112\h2112_0000.nd4.51" ; ~1 GB each
f2="D:\mydocs\data\hrsc\lev4\2123\h2123_0000.nd4.50" ;
a=bytarr(2000,2000)
for j=0,5 do begin
distance=(long([0,1e3,5e5,1e6,1e7,1e8]))[j]

s1=systime(/sec)
for i=0,9 do begin
openr,3,f1
point_lun,3,i*distance
readu,3,a
close,3
openr,3,f2
point_lun,3,i*distance
readu,3,a
close,3
endfor
s2=systime(/sec)
print, "repeat open:",s2-s1

s1=systime(/sec)
openr,1,f1
openr,2,f2
for i=0,9 do begin
point_lun,1,i*distance
readu,1,a
point_lun,2,i*distance
readu,2,a
endfor
close,1
close,2
s2=systime(/sec)
print, "single open:",s2-s1

print
endfor
end

IDL> filetest
repeat open: 0.12500000
single open: 0.094000101

repeat open: 0.10899997
single open: 0.078000069

repeat open: 0.14100003
single open: 0.12500000

repeat open: 0.14100003
single open: 0.13999987

repeat open: 0.14100003
single open: 0.12500000

repeat open: 0.15599990
single open: 0.12500000

IDL> filetest
repeat open: 0.13999987
single open: 0.094000101

repeat open: 0.093999863
single open: 0.078000069

repeat open: 0.14100003
single open: 0.13999987

repeat open: 0.14100003
single open: 0.14000010

repeat open: 0.15700006
single open: 0.13999987

repeat open: 0.14100003
single open: 0.14100003

and with the blocks reversed:

IDL> filetest
single open: 0.10899997
repeat open: 0.11000013

single open: 0.078000069
repeat open: 0.092999935

single open: 0.12500000
repeat open: 0.15700006

single open: 0.12500000
repeat open: 0.15599990

single open: 0.12500000
repeat open: 0.15599990

single open: 0.12500000
repeat open: 0.14100003

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[Message index]

		maximum LUN By: greg.addr on Mon, 24 November 2008 06:38
		Re: maximum LUN By: greg.addr on Tue, 25 November 2008 04:31
		Re: maximum LUN By: R.Bauer on Tue, 25 November 2008 04:10
		Re: maximum LUN By: greg.addr on Tue, 25 November 2008 02:55
		Re: maximum LUN By: R.Bauer on Tue, 25 November 2008 00:34
		Re: maximum LUN By: Jeremy Bailin on Mon, 24 November 2008 19:46
		Re: maximum LUN By: greg.addr on Mon, 24 November 2008 10:33

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