And while you are there: Such a setup usually allows using SSDs as a CacheCade layer through the RAID controller, making bcache superfluous. A disk cache can also be a specified portion of random access memory (RAM). Today, the disk cache is usually included as part of the hard disk. I suggest putting the SSDs into a battery backed hardware RAID before using write-back mode. A disk cache is a mechanism for improving the time it takes to read from or write to a hard disk. Please take into account that introducing a storage layer like LVM oder MD between bcache and the hardware can or probably will modify write guarantees for bcache - thus in that case you should not use write-back mode of bcache as that setup can lead to servere structural problems within bcache at reboot, shutdown, and clearly powerloss, and you don't want to have outstanding writes in that case. This data is stored until its time to live (TTL), which indicates how long content needs to be cached for, expires or the devices disk or hard drive cache. I figure you want to go with the reliable choice if you are backing a 12 TB data volume with it. Keep in mind that you may want to have at least one mirror or parity in your SSD RAID if you prefer reliability over pure speed. But you are free to arrange your SSDs in a RAID-0, RAID-1, or RAID-5, initialize the caching volume on this volume set and attach your backends to it. The bcache documentation clearly states that you can use one caching device for multiple backends but not vice versa (at least not yet).

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