Re: How long will a shrinkfs take?

[David Greaves <david@dgreaves.com>]

Alex Zarochentsev wrote:

>On Thu, Jun 10, 2004 at 09:13:35PM +0100, David Greaves wrote:
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>>Hi
>>
>>I have a 1Tb reiserfs that I want to shrink to 500Gb
>>400Gb of data is used.
>>
>>Any estimates as to how long this will take?
>>Sustained I/O is about 33Mb/s at the fs level, 44 Mb/s at the lv level 
>>and 65Mb/s at the md0 level.
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>ReiserFs shrinker reads all tree nodes as fsck does (reiserfsck --check may be
>used for rough estimation) plus shrinker writes relocated nodes (this highly
>depends on how many nodes are above 500GB boundary).
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OK -  well I know that fsck --check is of the order of minutes rather 
than hours (did that rather too recently ;) )

So if I asume even spread, 50% is above so 200 Gb needs reading + then 
writing so say 1Gb/min = 3-4 hours

OK ta.

BTW, is resizefs safely interruptible? So can I run it for a couple of 
hours, interrupt, fsck, remount and do it again?
(The system's in use and I only get short windows when I can do this 
kind of thing)
I understand that if this happens the fs won't have been resized.

I envisage the behaviour to be:
1 calc new top boundary
2 scan for files (nodes) with data above boundary
3 foreach file
3.1 copy data below boundary
3.2 change node to reflect new position
3.3 mark old space as free
4 set new top boundary

most of the time being spent in 3.

David

>Anyway running reiserfsck --check before shrinking is a good practice.
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>>(I didn't expect the fs to be so slow so I'm going to try a few tuning 
>>params on the new 500Gb space before copying over the data and growing 
>>back to a Tb)
>>
>>Is it proportional to the amount of shrinkage (ie 2 hrs to reduce by 
>>50G, 20 hrs to reduce by 500Gb)
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>>David
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