Everyone's predisposed that "mainframes are obsolete", but why not use a mainframe?
I mean, no one except for banks can afford one, let alone make back on opex or capex, and so we all resort to MySQL on Linux, but isn't the cost the only problem with them?
Banks smaller than the big ~5 in the US cannot afford anything when it comes to IT infrastructure.
I am not aware of a single state/regional bank that wants to have their IBM on premise anymore - at any cost. Most of these customers go through multiple layers of 3rd party indirection and pay one of ~3 gigantic banking service vendors for access to hosted core services on top of IBM.
Despite the wildly ramping complexity of working with 3rd parties, banks still universally prefer this over the idea of rewriting the core software for commodity systems.
Density is also bad. You spend 4 full racks and get 208 cores. Sure, they might be the fastest cores around, but that gets you only so far when even off-the-shelf Dell server has 2x128-192 cores in 1U server. Similarly 64 TB of RAM is a lot, but that same Dell can have 3 TB of RAM. If I'm reading the specs correctly (they are bit confusing), z17 has only 25G networking (48 ports); the Dell I'm checking can have 8x200G network ports and can also do 400G networking. So the single 1U commodity server has more network bandwidth than the entire 4 rack z system.
Sure, there will be lot of overhead in having tens-hundreds of servers vs single system, but for lots of workloads it is manageable and certainly worth the tradeoff.
Take a look at the cache size on the Telum II, or better yet look at a die shot and do some measuring of the cores. Then consider that mainframe workloads are latency sensitive and those workloads tend to need to scale vertically as long as possible.
The goal is not to rent out as many vCPUs as possible (a busines model in which you benefit greatly by having lots and lots of small cores on your chip). The goal for zArch chips is to have the biggest cores possible with as much area used for cache as possible. This is antithetical to maximizing core density, and so you will find that each dual chip module is absolutely enormous, and that each core takes up more area in the zArch chips than in x86_64 chips, and that those chips therefore have significantly less core density.
The end result is likely that the zArch chips are going to have much higher single thread perf. Whereas they will probably get smacked by say a Threadripper on multithreaded workload where you are optimizing for throughout. This is ignoring intricacies about vectorizatiln and what can / can't be accelerated and whether or not you want binary or decimal floating point and other details and is a broad generalization about the two architectural general performance characteristics.
Likewise, the same applies for networking. Mainframe apps are not bottlenecking on bandwidth. They are way less likely to be web servers dishing out media for instance.
I really dislike seeing architectures compared via such frivolous metrics because it demonstrates a big misunderstanding of just how complex modern CPU designs are.
A Rockhopper 4 Express, a z16 without z/OS support (running Linux) was in the mid 6 digits. It's small enough to co-locate on a rack with storage nodes. While z/OS will want IBM storage, Linux is much less picky.
IBM won't release the numbers, but I am sure it can host more workloads in the same chassis than the average 6-digit Dell or Lenovo.
Not the only problem with them. Not as easy to find skilled staff to operate them. Also, you become completely dependent on IBM (not fully terrible -- it's a single throat to choke when things go wrong).
I mean, no one except for banks can afford one, let alone make back on opex or capex, and so we all resort to MySQL on Linux, but isn't the cost the only problem with them?