1
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- So you might be wondering.

2
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Dirty cache.

3
00:00:10,860 --> 00:00:12,720
Alright, well what are you going to do

4
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in a situation like that?

5
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Well, I would suggest
cctl -a | grep dirty.

6
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And look at that.

7
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There we have all the dirty parameters.

8
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These dirty parameters have to deal

9
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with dirty cache.

10
00:00:28,080 --> 00:00:30,750
And dirty cache is an area of memory

11
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where modified blocks are stored

12
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before they are committed to disk.

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That's all pretty technical,

14
00:00:35,940 --> 00:00:39,450
but what we need is dirty
writeback centisecs.

15
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And we need that to be set to 60 seconds.

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But hang on, what's a cenitsec?

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Well that's a 100th of a second.

18
00:00:48,240 --> 00:00:51,570
So if we need it to
write every 60 seconds,

19
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then the writeback centisecs
would be written to 6,000.

20
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How do we do that?

21
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Well simple, echo 6,000
> /proc/sys/vm/dirty

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writeback centisecs.

23
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And now we can verify that.

24
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And in order to verify,

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let's just do a cat on this fella.

26
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And there we can see that indeed it is set

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to 6,000 right now.

28
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So, so far so good.

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How are we going to make it persistent?

30
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Well, we are going to make that persistent

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by using echo dirty.

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Oops, almost wrong echo
vm.dirty_writeback_centisecs

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is 6,000 > /etc/sysctl.d/dirty.conf.

34
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So vm.dirty writeback centisecs,

35
00:02:03,540 --> 00:02:04,860
what's the logic behind it?

36
00:02:04,860 --> 00:02:06,720
Well, vm, that's the directory

37
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and dirty writeback centisecs,

38
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that's a parameter that we want to set.

39
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So 6,000 and we write it to etc sysctl.d.

40
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Whatever dirty.conf.

41
00:02:18,900 --> 00:02:20,820
The name of that file
is not very important.

42
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The only requirement is that
it should be ending in .conf.

43
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And right, that is making
sure this is working.

44
00:02:29,250 --> 00:02:32,760
But there is just one thing
that we need to configure.

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We have now configured the kernel

46
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to start a threat every 60 seconds

47
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that will commit dirty cache.

48
00:02:42,750 --> 00:02:46,380
But there is also the
dirty expired centisecs

49
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and that is set to a smaller value.

50
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And that effectively is not going to work.

51
00:02:50,520 --> 00:02:54,926
So if you want to set the
dirty writeback centisecs

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to 6,000, then dirty expired
centisecs should least be 6,001

53
00:03:01,740 --> 00:03:03,810
because otherwise you
would have the problem

54
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that your dirty caches
expired after 30 seconds.

55
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But the dirty writeback centisecs demon

56
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only comes around every 60 seconds.

57
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That doesn't work because then
we would have expired cache

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for 30 seconds.

59
00:03:17,070 --> 00:03:19,800
And that's why this value
needs to be bigger as well.

60
00:03:19,800 --> 00:03:21,810
So let's take care of that also.

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Echo vm.dirty expire centisecs is 9,000.

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Double redirect to append
and not to overwrite,

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to etc/sysctl.d/dirty.conf.

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And now we check etc/sysctl.d/dirty.conf.

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Which has the parameters.

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00:03:57,270 --> 00:04:02,270
And we can use sysctl -p,
on etc/sysctl.d/dirty.conf.

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And that's going to make
them effective immediately.

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And that's all.