Re: How long will a shrinkfs take?

[Alex Zarochentsev <zam@namesys.com>]

On Fri, Jun 11, 2004 at 09:29:11AM +0100, David Greaves wrote:
> Alex Zarochentsev wrote:
> 
> >On Thu, Jun 10, 2004 at 09:13:35PM +0100, David Greaves wrote:
> > 
> >
> >>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.
> >>   
> >>
> >
> >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).
> > 
> >
> 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)

no. interrupting it is not safe.  fs errors are not so serious, but bitmap content does not
match relocated tree so fsck would suggest --rebuild-tree.

> 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

it scans internal reiserfs tree, not fs tree.

> 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.
> >
> > 
> >
> >>(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)
> >>   
> >>David

-- 
Alex.