should actually think carefully about what you’re doing and make sure that you’re doing all three.

GANGER Your choice for what you’re doing for any one of the three might be to do nothing, but it should be an explicit choice, not an implicit one.

RIEDEL And the other way around. When we’re talking about energy efficiency, being efficient about copies, and not allowing things to leak, then you want to think explicitly about why you are making another copy. BREWER Which copies do you really not want to lose? I differentiate between master copies, which are the ones that are going to survive, and cache copies, which are intentionally transient.

GANGER For example, if you’re running an organization that does software development, the repository—CVS (Concurrent Versions System), SVN (Subversion), whatever it is you’re using—is much more important than the individual copies checked out to each of the developers. BREWER It’s the master copy. You’ve got to treat it differently. No one can weaken your master copy.

CREEGER I know that the first CAD systems were developed for and by computer people. They did them for IC chip and printed circuit-board design and then branched out to lots of other application areas.

Is the CVS main development-tree approach going to be applicable to lots of different businesses and areas for storage problems, or do you think the paradigm will be substantially different? GANGER It will absolutely be relevant to lots of areas. BREWER I think most systems have cache copies and master copies. GANGER In fact, all of these portable devices are fundamentally instances of taking cached copies of stuff. BREWER Any device you could lose ought to contain only cache copies. SELTZER Right, but the reality of the situation is that there are a lot of portable devices you can lose that are the real copy. We’ve all known people who’ve lost their cellphones and with them, every bit of contact information in their lives.

CTO Roundtable

S TOR AGE

GANGER They learn an important lesson, and it never happens to them again.

SELTZER No, they do it over and over again, because then they send mail out to their Facebook networks that says, “Send me your contact information.”

CREEGER They rebuild from the periphery.

BREWER The periphery is the master copy; that’s exactly right.

CREEGER We’ve talked about security and storage infrastructure. We’ve touched on copyright, archival solutions, and talked a lot about energy. We’ve talked about various architectures and argued passionately back and forth between repositories and the free cloud spirit.

Storage managers have a huge challenge. They don’t have the luxury of taking the long view of seeing all these tectonic forces moving. They have to make a stand today. They’ve got a fire hose of information coming at them and they have to somehow structure it to justify their job. They have to do all of this, with no thanks or gratitude from management, because storage is supposedly a utility. Like the lights and the plumbing, it should just work. KLEIMAN They have a political problem as well. The SAN (storage area network) group will not talk to the networking group. The backup group is scared that their jobs are going to go away. Looking at the convergence of technologies, even for something simple like FCoE (Fibre Channel over Ethernet), the SAN Fibre Channel people are circling the wagons. CREEGER Or iSCSI over 10-gigabit Ethernet. KLEIMAN Absolutely. There are a lot of technical issues involved, but there are very serious people and political issues as well. Q

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This article appeared in print in the September 2008 issue of Communications of the ACM.

40 November/December 2008 ACM QUEUE

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