4 HDDs can do 200-400MB/s _sequential_ IO, 1 modern SSD can do 150-200MB/s _random_ IO and 400MB/s sequential IO while 4 HDDs would have a hard time doing IIRC more than 8MB/s random IO

Urm what? A modern NVMe drive will sustain ~2 GB/sec write.

(See e.g. https://cdn.mos.cms.futurecdn.net/Ko5Grx7WzFZAXk6do4SSf8-128..., from Tom's Hardware)

I recently bought an external 32GB SLC SSD (in the form factor of an USB pendrive). Its random read/write speeds are quite insane (130+ MB/s both) while consumer SSDs like the Samsung 850 Evo barely manage 30 MB/s read/write. It's also advertised as very durable.

I plan on using a couple of those as ZFS metadata and small block caches for my home NAS, we'll see how it goes but people generally and universally praise the SLC SSDs for their durability.

> You're best bet for long-term reliability is to buy much more capacity than you need and try not to exceed >50% capacity for high write frequency situations. I keep an empty drive around to use as a temp directory for compiling, logging, temp files, etc.

That's likely true. I am pondering buying one external NVMe SSD for that purpose exactly.

It's actually not better tech, instead it's more complicated, more error prone and less durable ways to use the same technology that produces more space for a lower price. MLC is pretty much okay but TLC is a little too fragile and low performance in my opinion. I prefer spinning HDD's over QLC since the spinning drives have predictable performance.

And logging all of those unit tests associated with all of those builds (and rolling over those logs with TRACE level debugging).

Every build gets fully tested at maximum TRACE logging, so that anyone who looks at the build / test later can search the logs for the bug.

8TBs of storage is a $200 hard drive. Fill it up, save everything. Buy 5 hard drives, copy data across them redundantly with ZFS and stuff.

1TBs of SSD storage is $100 (for 4GBps) to $200 (for 7GBps). Copy data from the hard drive array on the build server to the local workstation as you try to debug what went wrong in some unit test.