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Re: sparsify - utility to punch out blocks of 0s in a file

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: sparsify - utility to punch out blocks of 0s in a file
From: Raghavendra D Prabhu <raghu.prabhu13@xxxxxxxxx>
Date: Sun, 5 Feb 2012 20:35:44 +0530
Cc: ext4 development <linux-ext4@xxxxxxxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
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* On Sat, Feb 04, 2012 at 02:10:30PM -0600, Eric Sandeen <sandeen@xxxxxxxxxx> 
On 2/4/12 2:04 PM, Eric Sandeen wrote:
Now that ext4, xfs, & ocfs2 can support punch hole, a tool to
"re-sparsify" a file by punching out ranges of 0s might be in order.

Gah, of course I sent the version with the actual hole punch commented out ;)
Try this one.

[root@inode sparsify]# ./sparsify -v fsfile
blocksize is 4096
orig start/end 0/536870912/0
new start/end/min 0/536870912/4096
punching out holes of minimum size 4096 in range 0-536870912
punching at 16384 len 16384
punching at 49152 len 134168576
punching at 134234112 len 134201344
punching at 268455936 len 134197248
punching at 402669568 len 134201344
[root@inode sparsify]#

Hm but something is weird, right after the punch-out xfs says
it uses 84K:

[root@inode sparsify]# du -hc fsfile
84K     fsfile
84K     total

but then after an xfs_repair it looks saner:
# du -hc fsfile
4.8M    fsfile
4.8M    total

something to look into I guess... weird.

xfs mailing list

So I tried with both resparsify and with cp --sparse, the results before xfs_repair looks different (5 extents vs 1) but after that it looks similar (5 extents vs 4)

Raghavendra Prabhu
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