The Cyrus IMAP server has a "split metadata" mode which supports this configuration. Very nice if you are running a mail server of any significant size.
* VMWare uses this as the root of their vSAN technology.
* Nimble and other storage appliance manufacturers use a bank of SSDs to cache frequently-read data, and have layers of fast- and slow-HDDs to store data relative to its access frequency.
* Nimble and other storage appliance manufacturers use a bank of SSDs to cache frequently-read data, and have layers of fast- and slow-HDDs to store data relative to its access frequency.
* Hybrid HDDs have been around for years.