VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 5
Storage Checkpoints
Storage Checkpoint Administration
60
Converting a Data Storage Checkpoint to a Nodata Storage Checkpoint
A nodata Storage Checkpoint does not contain actual file data. Instead, this type of Storage Checkpoint
contains a collection of markers indicating the location of all the changed blocks since the Storage Checkpoint
was created (see “Types of Storage Checkpoints” on page 55 for more information).
You can use either the synchronous or asynchronous method to convert a data Storage Checkpoint to a nodata
Storage Checkpoint; the asynchronous method is the default method. In a synchronous conversion, fsckptadm
waits for all files to undergo the conversion process to “nodata” status before completing the operation. In an
asynchronous conversion, fsckptadm returns immediately and marks the Storage Checkpoint as a nodata
Storage Checkpoint even though the Storage Checkpoint’s data blocks are not immediately returned to the
pool of free blocks in the file system. The Storage Checkpoint deallocates all of its file data blocks in the
background and eventually returns them to the pool of free blocks in the file system.
If all of the older Storage Checkpoints in a file system are nodata Storage Checkpoints, use the synchronous
method to convert a data Storage Checkpoint to a nodata Storage Checkpoint. If an older data Storage
Checkpoint exists in the file system, use the asynchronous method to mark the Storage Checkpoint you want
to convert for a delayed conversion. In this case, the actual conversion will continue to be delayed until the
Storage Checkpoint becomes the oldest Storage Checkpoint in the file system, or all of the older Storage
Checkpoints have been converted to nodata Storage Checkpoints.
NOTE You cannot convert a nodata Storage Checkpoint to a data Storage Checkpoint because a
nodata Storage Checkpoint only keeps track of the location of block changes and does not save
the content of file data blocks.
Difference Between a Data and a Nodata Storage Checkpoint
The following example shows the difference between data Storage Checkpoints and nodata Storage
Checkpoints:
Step 1. Create a file system and mount it on /mnt0:
# mkfs -F vxfs /dev/vx/rdsk/test0
version 4 layout
11845780 sectors, 5922890 blocks of size 1024, log size 1024
blocks unlimited inodes, largefiles not supported
5922890 data blocks, 5920314 free data blocks
181 allocation units of 32768 blocks, 32768 data blocks
last allocation unit has 24650 data blocks
# mount -F vxfs /dev/vx/dsk/test0 /mnt0
Step 2. Create a small file with a known content. Create a Storage Checkpoint and mount it on
/mnt0@5_30pm:
# echo "hello, world" > /mnt0/file
# fsckptadm create ckpt@5_30pm /mnt0
# mkdir /mnt0@5_30pm
# mount -F vxfs -o ckpt=ckpt@5_30pm \
/dev/vx/dsk/test0:ckpt@5_30pm /mnt0@5_30pm
Step 3. Examine the content of the original file and the Storage Checkpoint file:
# cat /mnt0/file
hello, world
# cat /mnt0@5_30pm/file
hello, world
Step 4. Change the content of the original file: