Chapter 3 DXi3500 and DXi5500 Remote Management
Data Services
Quantum DXi3500 and DXi5500 User’s Guide
103
• The critically low filesystem capacity threshold is 250 GB. When the
free filesystem capacity drops below this level, the system transitions
to
critically low filesystem handling
.
• The threshold for transitioning out of
critically low filesystem capacity
handling
and back to normal operations is 260 GB.
If the system is operating in
critically low filesystem handling
mode:
• VTL tape cartridge writing is not operational
• NAS share writing is not operational
• Replication to this system is not allowed and is paused automatically
• Truncation of all deduplicated files will proceed, regardless of policy
Space Reclamation
3
The block pool data area of both the DXi3500 and DXi5500 systems is
used to store tags that reference deduplicated and replicated data. Tags
are used to rebuild a deduplicated file if it needs to be recovered. If this
deduplicated or replicated data has been deleted from the system, the
tags need to be removed from the block pool so the space can be used for
additional reference tags.
In the DXi3500 and DXi5500 systems, there are two processes that are
used to remove unused reference tags:
•
Reconciliation
- The reconciliation process prepares a list of candidate
tags (including reference counts for those tags) to be discarded. These
tags represent de-duplicated files that have been deleted from the
filesystem or replication sets that have been deleted. Reconciliation
takes a few minutes on systems that will not replicate data to target
systems or receive replicated data from sources. Reconciliation may
take several hours on systems that are replication targets (they must
wait for replications in progress to complete).
•
Reclamation
- The reclamation process reviews the list of discarded
candidate tags prepared by reconciliation and deletes the tag as many
times as required (i.e., until its reference count is zero). Reclamation
may take anywhere from a few minutes to a few days, depending on
the amount of de-duplicated data to be discarded.
When a tag is deleted, the reference counts of the blocklets referenced by
it are reduced. When the count of a blocklet becomes zero, the blocklet is