You
can have a mix of thin-provisioned and
fully allocated volumes in FlashCopy® mappings.
One common combination is a fully allocated source with a thin-provisioned target, which enables the target to consume a smaller amount
of real storage than the source.
For best performance, the
grain size of the thin-provisioned volume must
match the grain size of the FlashCopy® mapping.
However, if the grain sizes are different, the mapping still proceeds.
Consider the following information when you create your FlashCopy® mappings:
- If you are using a fully allocated source with a thin-provisioned target,
disable background copy and cleaning mode on the FlashCopy® map by setting both the
background copy rate and cleaning rate to zero. Otherwise, if these features are enabled, all the
source is copied onto the target volume. This causes the thin-provisioned volume to either go offline or to grow as
large as the source.
- If you are using only thin-provisioned source, only the space that is used on
the source volume is copied to the target volume. For example,
if the source volume has a virtual size of 800 GB and a real size of 100 GB of
which 50 GB is used, only the used 50 GB are copied.
- A FlashCopy® bitmap
contains one bit for every grain on a volume.
For example, if you have a thin-provisioned volume with
1 TB virtual size (100 MB real capacity), you must have a FlashCopy® bitmap
to cover the 1 TB virtual size even though only 100 MB of real capacity
is allocated.