Dear Bacula developers, A few years ago I deployed IBM Tivoli Storage Manager in the company I worked for at the time. Since then I've never really encountered a backup product that could match it in terms of speed or resource utilization, which can be entirely attributed to the "progressive incremental" backup strategy it uses. A file is never transferred over the network twice, TSM always takes incremental backups and keeps track of files it already has somewhere in its backup pool by using a relational database (IBM DB2 since TSM version 6). For a longer explanation, see
https://agora.cs.illinois.edu/display/tsg/Progressive+Incremental+Backups+explained Only new files are transferred to backup storage, files which have disappeared from the host since the previous backup are marked inactive and eventually purged from backup storage depending on the defined retention policies. It backs up to disk at night for speed, and transfers from disk to tape during working hours in a FIFO manner. This way restores are often almost instantaneous because the recent backup data is still on disk. Other daytime tape maintenance operations involve the creation of an off-site copy of the primary storage pool tapes (which are always on-line (!), your tape library must be large enough to accomodate this), reclamation (freeing tapes with mostly expired data) and collocation (moving data from a specific host on as least tapes as possible). The system works really well. Unfortunately no other backup product that I know of implements the same backup strategy. As a side effect, there is no real competition in this space and the licensing costs of TSM aren't pretty... My current employer isn't a TSM shop and as I'm not exactly thrilled with our current backup solution, I'm looking at affordable TSM alternatives but it appears that there just aren't any. I hoped that Bacula's new "basejob" deduplication feature would start offering something in this direction (as files in a basejob are only backed up once), but now that I've read a bit more about it, it doesn't seem to do what I hoped for. :-( What could be the reason no other companies or open source projects go in this direction? There are great open source databases, there are great open source backup projects, but there are none which attempt to forge these technologies into an "always incremental" backup product (or "enterprise class data management system" as some prefer to call it...). Best regards, Pascal P.S. The following document is a great introduction to TSM concepts: http://www.redbooks.ibm.com/redpapers/pdfs/redp0044.pdf
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