zfs discuss - Jan 2007 - Can you turn on zfs compression when the fs is already populated?

I have an 800GB raidz2 zfs filesystem.  It already has approx 142Gb of data.
Can I simply turn on compression at this point, or do you need to start 
with compression
at the creation time?  If I turn on compression now, what happens to the 
existing data?

Thanks,

Neal

>I have an 800GB raidz2 zfs filesystem.  It already has approx 142Gb of data.
>Can I simply turn on compression at this point, or do you need to start 
>with compression
>at the creation time?  If I turn on compression now, what happens to the 
>existing data?
Yes.  Nothing.

Casper

Neal Pollack wrote:
> I have an 800GB raidz2 zfs filesystem.  It already has approx 142Gb of
> data.
> Can I simply turn on compression at this point, or do you need to start
> with compression at the creation time?
As I understand it, you can turn compression on and off at will.
Data will be written to the disk according to the compression mode,
and either compressed or uncompressed blocks can be read regardless
of the setting.

  If I turn on compression now, what
> happens to the existing data?
Existing (uncompressed) data will remain uncompressed until it is re-written,
at which point it may be compressed.

Dana

I''ve used the COMPRESS feature for quite a while and you can flip back
and forth without any problem. When you turn the compress ON nothing happens to
the existing data. However when you start updating your files all new blocks
will be compressed; so it is possible to have your file be composed of both
compressed and uncompressed blocks!
 
 
This message posted from opensolaris.org

For what it''s worth, there is a plan to allow data to be scrubbed so
that
you can enable compression for extant data. No ETA, but it''s on the
roadmap.

In fact, I was recently reminded that I filed a bug on this in 2004:

  5029294 there should be a way to compress an extant file system

Adam

On Wed, Jan 24, 2007 at 06:50:22PM +0100, Casper.Dik at sun.com
wrote:
> 
> >I have an 800GB raidz2 zfs filesystem.  It already has approx 142Gb of
data.
> >Can I simply turn on compression at this point, or do you need to start
> >with compression
> >at the creation time?  If I turn on compression now, what happens to
the
> >existing data?
> 
> Yes.  Nothing.
> 
> Casper
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> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
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-- 
Adam Leventhal, Solaris Kernel Development       http://blogs.sun.com/ahl