i do this on my synoligy using btrfs. i’m still not convinced SSD caching gives any benefit for a home user. 5 spindle drives can already read and write faster than line rate on the NIC (1gbe) so what is the point of adding another failure point?

> 5 spindle drives can already read and write faster than line rate on the NIC (1gbe) so what is the point of adding another failure point?

SSDs are more about latency than throughput. (And who wants to deal with five spindle drives in a desktop computer?)

In any case, in my case I had the SSD first and bought the HDD to expand my storage capacity.

I don't know whether your use case cares about latency, or about the number of drives. Your trade-offs might be different from mine.

You manage 5 discs in a device because you care about data protection, being safer than a single disc.

Yes SSDs in theory are faster but you are only as fast as your slowest link, which is the spindle drive. so that cache is a buffer only for frequently read data. in home environments they’re next to useless. in enterprises they’re certainly useful.

> Yes SSDs in theory are faster but you are only as fast as your slowest link, which is the spindle drive. so that cache is a buffer only for frequently read data. in home environments they’re next to useless.

If you check the numbers I gave above, I have 2 TiB SSD and 8 TiB hard disk. My 'frequently read data' is basically all the data I care about accessing. The other 8 TiB is mostly for eg steam games I installed and forgot about or for additional backups of some data from cloud services, like Google Photos. These are mostly write-once-read-never.

And eg if I happen to access a steam game that's currently on the HDD, it will quickly migrate to the SSD.

My 'working set' of data is certainly smaller than 2 TiB.

Five disks are safer than a single disk (if you store things multiple times or with erasure coding), but if you stick all five disks in a single device, the safety gains are rather more limited.

yea so again the single spindle drive is slowing it down. the spindle drive doesn’t get faster because it has an SSD, if you read something from the spindle it will read at the same speed the spindle is rated at. after it’s loaded into the SSD then it’s faster. but only then

> Five disks are safer than a single disk (if you store things multiple times or with erasure coding), but if you stick all five disks in a single device, the safety gains are rather more limited.

There are devices called storage servers or NAS. this idea of not putting more than one spindle in a machine is foreign to me.