I had the good fortune last week to spend two days in the company of a dozen independent bloggers, pundits, geeks and other thought leaders in storage, networking and virtualization at GestaltIT's Seattle tech field day. We sat, not so politely, through the usual death by PowerPoint and live demos from a series of vendors ranging from those I knew well (F5 and Compellent) to those like Nimble Storage, a start-up brave enough to come out of stealth in front of the Tech Field Day crowd.
While Sharon Fisher broke the Nimble Storage news as it happened here, I found their story compelling enough that a deeper dive would be useful. Nimble's primary claim to fame is the combination of flash memory as a huge read and write through cache with 1TB SATA drives to create a high performance system that can not only act as a primary iSCSI array but also store enough snapshots to replace conventional backups.
The basic CS220 combines a 640GB flash cache with 12 1TB SATA drives for 9TB of useable capacity and what Nimble's folks claim is the equivalent of 108TB of backup data. Like StorWise or even NTFS, they do LZ style compression on data before saving it. They then use their own log-based file system that always writes full stripes to the RAID back end, making much random I/O--which SATA drives don't handle well--look more like sequential I/O, which SATA drives are pretty good at.
Nimble uses redirect on write snapshots, which unlike the more common copy on write variety, should have limited impact on performance even if you retain a large number of snapshots for a long time. Of course snapshots alone aren't a replacement for backups since an explosive power supply failure, or the like, that destroys the system also destroys the data and the snapshots. My friend W, Curtis Preston, who was also at the event, has written that a combination of snapshots and replication could replace daily backups, but it would still need a metadata index to help you find the version of a file you want to restore.
Today, Nimble doesn't quite allow you to replace your backup system. They can only replicate between two systems so you have to choose between a local copy for fast restores and a remote copy for disaster protection. They have promised cascading replication in a future version of the software.