Imagine my surprise upon discovering that the space reservation for LUN snapshots is 120%, instead of 20% to 30% for a file system. I think I understand why. I wonder what the practical field experience is with trimming that figure down to something the guy who paid for the NetApp will accept.
Specifically, if what is on the LUN is a relatively stable NTFS file system, is "blocks changed" similar enough to "files changed", or are there "catastrophic events" that go out and touch many disk blocks at once, thus mandating the huge space reservation?
If you under-allocate the reservation, then all disk blocks are suddenly written to, can you configure the NetApp to release the snapshots and commit the writes, or must it look like a premature disk full condition?
It seems like a much more economical path will be to ignore the SnapDrive approach, ignore snapshots, and just use Volume Shadow Copy on the windows servers hosting the filesystem. This would get my space reservation back down to 20% to 30%. Any thoughts?
Oh, a bonus question: I had a NetApp PS guy recommend 28-disk RAID-DP over 14-disk RAID-DP, saying that there is absolutely no significant difference in re-build time or any other down side. Any thoughts on that?
Thanks!
/// Rob