I went to a NetApp demo today, and they were trying desparately to show me where they competed with the Centerra.
First off, i think the demo went in the wrong direction.Â I am not the “average” customer, I wouldn’t have been there if I wasn’t interested, so it should have been very much less ‘sales-pitch’ and more nuts and bolts, ‘geeky details’.
My first question, and one that they were not able to answer was about the compliance clock.
First off, the coolest part of the netapp is that the structure of the fileserver itself is stored within the metadata on the disks, as well as in the processor.Â This means that (in theory, because I’ve never seen it happen) you can pull the disks out of one filer, put them in a new one, power it up, and have everything exactly as it was when you shut down the original.
Now this is a good thing, except that I understand the compliance clock exists and has to be initialized within the processor.Â Now once it’s set it is locked.Â The gentleman who ran the demo even admitted he doesn’t know of a way to “clear” it, though I’m sure it can be done through a fairly routine clearing of the NV ram in the storage processor.
So if you’ve got data on a raid group that can’t be deleted, you shut the array down, move the disks to a new array, and boot it.Â You then go and initialize and set the compliance clock in the new unit to 30 years ahead and poof, you can now delete data from the disks.
Yes – it’s an unrealistic scenario, but I have always pictured my job in situations like this to be to find the hole in the ruleset and drive a truck through it.
if you can move the disks to a new array and tinker with the clock there, then it’s not a true compliance product.
Can anyone tell me if I’m off base?Â Is the compliance clock dependant on the disks as well as the array?
My second problem is the idea of “block-level” remote replication.Â The one thing I liked about the centerra is that it’s policy-based replciation is object based, meaning that when a file is replicated it’s pushed to the remote array.Â This, among other things, protects the integrity of the remote filesystem. (not that Centerra has a filesystem per-se)Â Block level writes, when interupted, can cause filesystem-wide corruption and other general weirdness.
On another (minor) point, the fact that replication is accomplished by reading the data just written to the disk, would double the IO load on the devices.Â (Why do it that way, when it could be simply written directly from cache to two locations…but that’s just crazy talk, right?)