Hello Collector,
First, let me say, that if you are going to be purchasing a new MSA like this then you may want to consider engaging the solution architecture resources of the HPE partner that you'll be purchasing from. I commend you for wanting to plan this out before purchasing and that is exactly what the SA resources should be able to help you do with much more attention and focus than you'll be able to get from a forum. I'll address as much as I can here:
1) Yes, my customers have had very good experience, and little trouble, with virtualization features on MSA. Performance tiering and caching are pretty much set it and forget it type of things on an MSA. However, as your dataset grows and workload changes, it never hurts to take a look once and a while and see if adding additional resources will help improve your setup. There are no daily knobs and dials to turn but definitely good to do some occasional assesments.
2) You mentioned not being able to afford any downtime. If that is truly the case then there may be better platforms for you in the HPE line. I know entire organizations that run on MSAs perfectly fine but, as you move throughout the HPE product line, you will find additional features and enhancements that will help reduce the exposure to downtime.
3) On an MSA with virtualized storage, you have a Pool A and Pool B; each assigned ownership to a seperate controller. You create virtual disk groups and assign them to a Pool. Once a pool has disk groups of different drive types assigned then you are "tiering". If you wish to have SSD in a virtual disk group then you need the performance tiering license (included on 20x2). A pool can be configured to use SSD as a cache or as a performance tier but not both. While you could have one pool caching and one tiering, it would not be recommended as it starts to get into that fine grain management and knob and dial type thing that I think you are looking to avoid.
4) While not 100% true in all cases, think of SSD caching on the MSA as sort of a poor man's tiering. It works well for people who don't want to make a substantial investment in SSD but still want some benefit from SSD. SSD Caching affects only random reads and requires 1 or 2 SSD disks per pool. Data is only copied to SSD and never permanetly lives there. So, RAID protection on a cache drive is not needed. So, out of the box, the 20x2 model can have an SSD cache on each pool. All writes will follow the normal onboard cache/drive process and sequential reads will come directly from disk.
5) Tiering allows us to introduce different performance levels of drives into the same pool. Typically we might see 10-15% SSD, 35-45% 10/15k, and the remaining as nearline. We would build a config needed based on initial capacity and theoretically only ever expand our lowest tier of drives as more capacity was needed. Writes and reads are automatically optimized with the hottest data living (not copied) on SSD, coldest on NL, and the rest in the middle. You do not need all three drive tiers but it is not generally considered best practice to have an SSD/NL setup. SSD/10k would generally be recommended in 2-tier setups. However, there may be very specific use cases where SSD/NL would be appropriate.
6) Spares are assigned globally and are available to replace a qualifying disk in any disk group or pool. In a tiering config, you can probably get away with 1 x SSD spare, maybe 1 x spare for every 12-24 10/15k drives, and 1 spare for every 12 ish NL drives. This is all personal preference and comfort. Always use RAID6 on nearline and considering using RAID6 on your 10/15k as well. If using RAID 5 on 10/15k, I would bump up the spare count.
7) Finally, regarding your layout. Best practice is to design a growth method and stick with it by adding disk groups that are as close as possible to your original disk group capacity and RAID layout. This will ensure that disk groups are properly balanced and perform at most efficient levels. You didn't mention capacity points so it's hard to really design out anything for you. If you choose tiering then I would start with a minimum of 7 x SSD's (2 x 2+1 plus spare in RAID 5). You can also do less and do high capacity drives and RAID1. Again, this all depends on the specifics of your requirements and budget. For your spinning tier I would go with a minimum of 13 drives (2 x 4+2 + 1 spare in RAID6). Depending on what you need for capacity/performance, this may be enough.
It sounds like you might have already referenced it but, if not, the best practice guide is a valuable resource at https://www.hpe.com/h20195/v2/GetPDF.aspx/4AA4-6892ENW.pdf or 2050 specific https://www.hpe.com/h20195/V2/getpdf.aspx/a00015961enw.pdf?ver=1.0
Mike
I work for HPE. The comments in this post are my own and do not represent an official reply from the company. No warranty or guarantees of any kind are expressed in my reply.
