[Ukfreebsd] Filesystem behaviour on filling

Jon Schneider jon at axismilton.ltd.uk
Thu Jun 11 14:41:04 BST 2015


Two years ago I posted about FreeBSD's unwillingness to clean up a known
inconsistent filesystem but here's a related problem.

In a Virtual(box) 10.1 installation with an emptyish 12GB I start filling
a filesystem with

cp /dev/zero huge &

(cp uses 4k blocks by default)

What I find is atrocious performance. I have checked using a W7 host, a
Linux host and a Linux guest doing the same test.

I would expect the thing to fill and cp to terminate with a message saying
so. What in fact happens is on this 12GB filesystem I get bored and go to
lunch.

The virtualbox host isn't doing any significant I/O

After lunch I find the cp still going, the console responsive to carriage
returns but shell stuck executing a "ls -lth" I asked for before I went
out.

I appreciate it's a virtual machine but it would surely be equally bad
using a network block device such as iSCSI.

What is going on ?

Jon



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