# btrfs with an SSD and a HDD

## daviessm

I have a computer with a small SSD and a huge HDD. The root filesystem is btrfs on the SSD and the HDD is used for backups and mythtv recordings. However, having recently migrated to a new platform my SSD isn't large enough to hold everything in /home any more.

What do you think is the best way to make efficient use of the space? I considered appending the disks into a btrfs volume but that would halve the data integrity. I've also thought about creating a volume of raid1 between part of the HDD and the SSD but can I tell it to use the SSD as a primary and copy the files to the HDD as sort of a backup to preserve the latency benefits that the SSD will provide?

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## ulenrich

Isn't there coming a btrfs feature to use SSD space a a hot-cache for some set of integrated volumes?

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## daviessm

I hadn't heard of that but I'm stuck on kernel 3.8 anyway (the box is an armv7 ODROID-X2).

A bit more information about my setup: The ODROID has an onboard SD card slot, in which I have a 64GB SDXC card. I have an external USB dock which holds a 1TB SATA HDD and another 32GB SD card.

My latest idea is to create a 96GB btrfs partition on the HDD and use btrfs raid1 over that and the two SD cards. That should mean I have all the data stored on the HDD and a copy spread over the two SD cards. Am I right in thinking that if any of the three devices failed, I'd still have a running system? Now, if the 64GB SDXC card failed then I'd lose the boot partition and it wouldn't be able to boot but if I recreated that, everything would still just work.

Or am I delusional?

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