Your description of how the IP4700's Snapshot copy-on-write mechanism works is right on. The original data is copied to a new location and the new
data
is written to the original block. Yes this compromises performance. Yes you have to allocate physical disk space to accomplish this. No you cannot shrink the amount of disk space you have allocated for this process if you find that it is too much.
Hmm, not according to a demo we had from EMC week before last. I grilled them pretty hard on that and they claimed that they updated the inode file only and did not copy blocks to another location.
Well, we have an eval unit coming in next week and I'll do some testing.
Regards
Martin Enterprise Storage/Enterprise Server Group mailto:martin.hughes@halliburton.com cellphone: +1 713 303 9214 office: +1 281 871 4124