file preallocation without unwritten flag being set

[Eric Sandeen]

p v wrote:
> 
> Hello,
> 
> I need to create large files fast without initializing them - in the
> past I used these steps -
> 
> mkfs -t xfs -f -d unwritten=0 /dev/sda1 mount -t xfs -o noatime
> /dev/sda1 /hay touch /hay/foo xfs_io /hay/foo xfs_io> resvsp 0 1024g 
> xfs_io> quit ls -i /hay/foo 131 /hay/foo umount /hay xfs_db -x
> /dev/sda1 xfs_db> inode 131 xfs_db> write core.size 1099511627776 
> core.size = 1099511627776 xfs_db> q

Is there a reason that you don't want the unwritten flag set?  (You know
that not using the unwritten extents feature exposes garbage from the
disk in this case?)

There may well be a legit reason but I just want to make sure you're
doing what you think you're doing :)

Thanks,
-Eric

> But unwritten=0 is failing as unrecognized option now (was it
> deprecated????) so I tried to clear the unwritten extent flag
> directly -
> 
> xfs_db> a u.bmbt.ptrs[1] xfs_db> write recs[1].extentflag 0 
> recs[1].extentflag = 1 xfs_db>
> 
> It just won't change to 0 - any way to do this? Or is there any
> straightforward way to preallocate a large file and set it's file
> size without the unwritten flags being turned on?
> 
> Thanks
> 
> Peter Vajgel
> 
> 
> 
> 
> 
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