> 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, As I understand it, inotify generates asynchronous events, which something else comsumes (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 frequent backups, 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 it is similar to DMAPI. ADM will be using DMAPI receive file modification events (among other event types), which based on policy will trigger archive requests to tape and/or disk archives. ADM will be only archiving whole files (not incremental just the incremental changes). 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 be more appropriate for disk archiving (due to tape load times and tape wear). 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. Keep in mind that CDP is not the design center here. If configured to approach CDP behavior on rapidly changing filesystem, one can imagine ADM 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/ (my apologies if this shows up multiple times – I tried replying to the email alias and it just said “An HTML attachment was scrubbed”) -Joe This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
