ext3 zerofree option and RedHat back port?

[Eric Sandeen]

Ulf Zimmermann wrote:

> Reason I asked is this. We use currently 3Par S400 and E200 as SAN
> arrays. The new T400 and T800 has a built in chip to do more intelligent
> thin provisioning but I believe even the S400 and E200 we have will free
> on the SAN level a block of a thin provisioned volume if it gets zero'ed
> out. Haven't gotten around yet to test it, but I am planning on. We are
> currently using 3 different file system types, one is a propriety from
> Onstor for their Bobcats (NFS/CIFS heads) where I believe I have
> observed just freeing of SAN level blocks. The two other are EXT3 and
> OCFS2.

Ok, so you really want to zero the unused blocks in-place, and e2image
writing out a new sparsified image isn't a ton of help.

The tool does that, I guess - but only on an unmounted or RO-mounted
filesystem, right?  (plus I'd triple-check that it's doing things
correctly, opening a block device and splatting zeros around, one hopes
that it is!)

But in any case the util itself is simple enough that building (or even
packaging) for fedora/EPEL should be trivial.

(FWIW, there is work upstream for filesystems to actually communicate
freed blocks to the underlying storage, just for this purpose...)

-Eric