update-prot command

The update-prot command toggles or displays the status of the file update protection scheme. When enabled, this feature globally protects all item updates so that a power-off condition does not cause a file inconsistency.


update-prot {(options}


options f Toggles update protection off.
n Toggles update protection on.

By default the update protection is on. If the user turns update-protection off, and later turns it back on, the user must use a flush command afterwards to be sure that all previous updates are written to disk.

If update protection is desired for selected files only, the user may disable the global update protection flag (with update-prot-off), and enable the protection on the selected files by changing attribute 1 of the D-pointers of those files to du. When all desired files have been changed to a du-type, the user must use a flush command to write all previous updates to the disk.

If update protection is desired for most of the system, but the user wishes to disable it on certain files, the user can change attribute 1 of the desired D-pointers to dn. These files are not protected irrespective of the global update-protection status.

Warning: To implement the update protection scheme, the system must ensure that all updates are done in a so-called atomic fashion. This means that the whole update either makes it to the disk or not. Because of this, it is necessary to force-flush pointer-items and overflow group items to disk at the time the item is written. Therefore, users may notice some performance decrease if this feature is active, and the system updates large pointer items (items with lengths greater than about 300,000 bytes) or normal items in badly sized files with groups exceeding about 20 frames. In this case, the files should be resized, or the user may turn off update protection by setting the first attribute of the selected D-pointer files to dn.