You mean the Clustra that was acquired by Sun and renamed HADB? I used it, and as far as I can remember, the HADB fault-tolerant story was that each node has a mirror that takes over if the first fails; and it's basically all in-memory. The Clustrix redundancy granularity is much finer, and everything is on disk.
Clustra/HADB did use disks (can't have all your data disappear if you turn off the cluster!) but a running system was in-mem in operation -- if your database was much bigger than the RAM available it was unusable. (I never used Hypra.)
Comments
You mean the Clustra that was acquired by Sun and renamed HADB? I used it, and as far as I can remember, the HADB fault-tolerant story was that each node has a mirror that takes over if the first fails; and it's basically all in-memory. The Clustrix redundancy granularity is much finer, and everything is on disk.
I never worked with one, but I believe the HyPra system included disks (as shown on page 148. http://books.google.com/books?id=KH_kfSsMu80C&pg=PA148 ). I recall it was one of the earlier systems to achieve high transaction rates by logging updates to memories of multiple replicas (described on page 181: http://books.google.com/books?id=KH_kfSsMu80C&pg=PA181 ).
Clustra/HADB did use disks (can't have all your data disappear if you turn off the cluster!) but a running system was in-mem in operation -- if your database was much bigger than the RAM available it was unusable. (I never used Hypra.)