Date: Tue, 20 Mar 2018 18:14:26 -0400 From: Zaphod Beeblebrox <zbeeble@gmail.com> To: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Intel RST disk formats and cache drives. Message-ID: <CACpH0Mcgsk8rERqVP9pdKoRMO0n0HPQUnbEr1_E%2B3iFGdd72TQ@mail.gmail.com>
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I see, and have used, the geom_raid bits to support Intel "software" RAID systems, but the support is imperfect. I have a laptop that has a rotating disk and an msata disk (for cache). I would like to use unused space on the msata disk for an installation of FreeBSD. However, FreeBSD doesn't see the "label" that uses the msata disk as cache. To try and figure things out more, I labelled an extra partition in windows on the msata drive and then booted FreeBSD. FreeBSD sees the extra partition, but not the cache partition. On further examination, it seems the Intel scheme uses blocks at the "end" of the disk and presents windows with a smaller disk. This squares with the system "C" disk. FreeBSD sees the GPT partition as corrupt because the "backup" doesn't exist. It does, but it's not at the "end" of the disk as FreeBSD sees it. So... when using the Cache, the intel driver in windows uses this labelling scheme on both disks. Has anyone looked at supporting this? Would we modify the existing graid to eat these disks, or some part of gpart/glabel? It doesn't exactly fit as there are also configurations where you have a RAID1 with a solid state cache drive. Is it possible we can support these configurations (at least as labels) without supporting the cache semantics?
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