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Can someone please point me to link, or just unambiguously say 'yes'
or 'no' to my question, if ZFS could produce a snapshot of whatever
type, initiated with a signal that in turn is derived from a change
(edit) of a file; like inotify in Linux 2.6.13 and above. Hi Uwe, I wasn't previously familiar with inotify, so I may be off here... But as I understand it, inotify generates asynchronous events, which something else consumes (e.g. A backup tool). I believe the asynchronous nature of inotify prevent it from enabling “true” CDP. i.e. It would enable very frequent backups, but there still may be rewrites occurring before the first async event is delivered & processed. But based on your later comments... I think you're just looking for very frequent backups, but not necessarily capturing every unique file version? You might want to look at the information we've starting posting about ADM (an HSM). There are two general use cases for ADM: a backup solution, and a disk extender. ADM will be using a subset of DMAPI to monitor file system activity. After skimming some brief info on inotify, I believe DMAPI is similar to inotify. ADM will be using this receive file modification events (among other event types), which based on policy will trigger archive requests to tape and/or disk archives. Note that ADM will be only archiving whole files (not incremental just the incremental changes). Additionally, since its an HSM, archived files may (based on policy, etc) be released from the file system. This is the “disk extender” part. Think of it as an “under the covers truncate” that frees the disk space. When the file data is accessed in the future, events trigger ADM to stage the file back in from the archives. Users would notice a delay (as it is staged in), but would not have to take explicit action to get the file data resident again. Releasing files will of course be optional. ADM could provide frequent backups, if configured to make archives soon after file modifications. Since we archive the whole file this would not be not appropriate for large files with frequent small changes. Also, frequent backups would only be appropriate for disk archiving (due to tape load times and tape wear). Keep in mind that CDP is not the design center here. If configured to approach CDP behavior on rapidly changing filesystem, one can imagine it hammering a filesystem and still not keeping up. Also, ADM archives are very different from ZFS snapshots. We have not yet defined how a user would explicitly access a specific archive. The expectation is, we'll provide a way to see all the versions we have for a file, and the user can tell us to either restore it over the current contents of the file, or restore to a new file. http://opensolaris.org/os/project/adm/WhatisADM/ -Joe |
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