DAOS and The Space Used Column

How it works:

One of the original features of the Notes Storage Facility (NSF file) was the ability to track the actual space within the file being consumed by data. Displayed as a percentage, the "Space Used" value (or "% Used" in Database Properties) gave users a way to gauge how much of the total physical byte size of an NSF file was actually being used to store data. This value was useful when implementing quotas or to see when additional space on the file system could be realized by the compaction of larger, "bloated" NSF files. The following is a graphical depiction of an NSF file with used space (black blocks) and free space (white blocks):



Here, Space Used would show that db.nsf is 76% used.

Presume that these blocks each represent 4096 bytes of data. Database db.nsf would have a physical size of 1,638,400 bytes where 24% (389,120 bytes) of that would be white space.

You could add a 320K attachment to db.nsf without increasing the physical size of db.nsf (that is, the NSF file will re-use its white space):



Now, db.nsf would have a space used of 96%.

With this notion of used space and the re-use of "free" space, the physical filesize of the NSF file would become a high water mark to increase in size only if necessary. With the continued addition and deletion of documents in the lifetime of the NSF file, "Space Used" became a means to gauge the current "water" level (data) with respect to that high water mark (physical file size).

It would also be used as means for enforcing quotas on NSF files when "Check space used in the file when adding a note" was used as the quota method. If space used was over a designated quota threshold, a note could not be added, the file would not be extended, and the user would see the appropriate error message.

Enter Domino Attachment and Object Service:

Problem #1: The Space Used before DAOS is enabled on a database is not consistent with that of the Space Used after DAOS is enabled on the database.

Using the initial graphical depiction of db.nsf with a Space Used of 76%:



Assuming that half of the 76% used was attachment data, when db.nsf is compacted to participate in DAOS (compact -c -daos on), you would not see this:




and a Space Used of 38%. Enabling DAOS and converting attachments requires a copy style compact, so what you would actually see is this:




The file db.nsf would have a new, smaller physical filesize of 626,688 bytes and 622,592 bytes worth of attachments would reside in the DAOS repository, for a total logical size of 1,249,280 bytes. Space Used would now read 99%, possibly 100%.

IMPORTANT: DAOS does not change how the value for Space Used is calculated and Space Used is completely unaware of DAOS attachments "linked" to db.nsf.

Problem #2: Space Used does not decrease as documents with large attachments are deleted.

Users will expect to see Space Used decrease when they delete documents containing large attachments; however, when using DAOS, this will not happen. After the deletion of 552,960 bytes worth of attachments, db.nsf would still show a Space Used of 99%:



The above deletion of attachments would not produce free space in the NSF file and a new Space Used of 11%:



IMPORTANT: Space Used deals exclusively with the physical NSF file.

With a portion of the NSF file's space now outside of the file, the feature can no longer accurately gauge the used space of what now represents a complete NSF file.

The Removal of the Space Used Column:

While the concept of the used space of an NSF file may have been useful with previous versions of Lotus Notes and Domino, as the product changes and new features are added, it is becoming increasingly less useful. Especially with DAOS in 8.5, Space Used has much less obvious meaning when it comes to a Notes Database. The Space Used column may still have meaning when it comes to a physical NSF file, but certainly not as it relates to total database file size, quota enforcement, and compaction. It is for these reasons that 8.5 saw the last of the Space Used column.