Remco Barendse redhat@barendse.to wrote:
That's not entirely correct. The 3Ware disks almost use standard raid format,
There is no "standard RAID format."
Different vendors -- be it hardware or FRAID -- as well OS software organizations use different offsets, blocking, etc... for RAID-0, 10, 3, 4, 5, etc... But the overwhelming majority of RAID implementations have a "meta-data block" or set of blocks that describe this organization. It's done so drivers, firmware or even other cards from the same vendor/code can read the disk organization.
The Device Mapper (DM) work is able to read some of these meta-data blocks to understand RAID-0, 10 and even "1e" (2 disc RAID-10, long story).
About the _only_ "industry standard" is RAID-1. I haven't seen a vendor yet who didn't do straight mirroring -- 1 sector to 1 sector.
it's just the raid block on each disk that is written at the end of the disk I believe instead of at the beginning.
Again, you are talking about the meta-data block(s). That's different. 3Ware adds those, yes. It's mainly for managing the disk. Most vendors do put them at the end, yes. But vendors differ on their meta-data blocks. But most have been reverse engineered and documented.
I'm talking about being able to take a standalone disk and put it into a RAID-1 array on a 3Ware card. You can because RAID-1, unlike RAID-0, 10 or 5 on a 3Ware card, does _not_ stripe data in 32KiB (default) blocks.
About a year a go we rescued all data from a series of PATA disks from a friend of mine when his 3Ware went bust. We were able to start the array in software raid with the right parameters. Google was my friend then
Was it RAID-1? Or RAID-10 or 5?
RAID-1 volumes are _extremely_easy_ to read.
RAID-0, 10 or (not yet?) 5 requires Device Mapper (DM) or another software implementation _must_ read the 3Ware meta-data blocks so it can understand the striping/blocking organization. Not being able to read the meta-data blocks will prevent you from finding the _exact_ striping positions and blocking size (32KiB is the default) for RAID-0, 10 and 5.
But RAID-1 is just straight mirroring. It's not as important if you can't read the meta-data block.