Trying to respond from my phone the last time, probably wasn't a good idea for such a lengthy message. Hopefully this message will help clarify things a little more for you, but if not please don't hesitate to ask additional questions.
You are correct, Data Progression is not a realtime process and does run on a schedule. The frequency schedule for Data Progression is not something that you can adjust. For the nearly 6 years I worked with the product, it was always once every 24 hours. The only tuning option you had was time of day it began, but the default was always 7:00PM. I've heard rumors that the frequency has been adjusted in the past year or so to accommodate SSD configurations, but that only adjusted it from being once every 24 hours to being something more like once every 4 hours. Again, there are no options for adjusting Data Progression to only run once every week or month.
Storage Profiles can be custom created once you change the system to "manual mode". Otherwise, you have access 4 for system created, unchangeable, profiles you can freely assign to volumes. To be honest the 4 system created Storage Profiles should cover more than 99% of all use cases. The default profile is called "Recommended (All Tiers)" and is what almost every volume created uses. However, there isn't anything to stop you from making whatever custom Storage Profile you'd like, but I'd highly recommend talking it over with someone well versed in Compellent before you do as the vast majority of customer issues I dealt with were because people wanted to overthink how to use the system and ultimately caused the system to perform worse than had they left it alone with defaults.
Data Progression doesn't exactly depend on Replays (snapshots), but its usefulness is highly improved when Replays are taken at least once per Data Progression cycle. I'm not really sure where to direct you for more information on this other than your Dell storage specialists or the Dell website. I'm sure Dell has come up with some nice marketing information by now that can explain it, but when I was at Compellent and Dell there really wasn't anything good and this was often a whiteboard discussion with customers. What you're looking for is the presentation called "The Day In The Life of a Page" and to be honest, Scott DesBles gave the best presentation of this over anyone I ever heard it from. Without trying to type the entire presentation up in this response, the best I can explain it is that with a snapshot you are locking all of the blocks (pages) as read only until they expire. Since the Storage Profile provides you with the option to store writable data differently than replay data you can configure the system to force writes to RAID 10 on a tier, but store replays at RAID 5/6 on the same tier. This may not sound like much, but what you get is extra disk space to store your data rather than only using RAID 10 without taking any major performance hits on writes or reads. If after the replay is taken a page is modified by a server, a new page is created and the active volume map is updated to reference the new page instead of the old. The key here being that the new page is written back into the system at RAID 10 and nothing has to be done to the old one. Within the Compellent system there are 3 types of pages:
- Active - these pages are writable
- Historical Accessible - these pages are read only, but still referenced by an active volume
- Historical Inaccessible - these pages are read only and only referenced by a replay (no active volume can access it)
If you understand and liked your Netapp systems, then you will probably really like the story of how Tegile works. However, I completely understand the criticality of good support and how challenging it can be when you're not in the same part of the world as vendor. Tegile does have teams in Europe and I'd be more than willing to get you in touch with them if you would like. Just send me a note and I'll pass along your contact info.
Aaron Gipson