[Bug 1251881] Re: dmraid-activate does not work on SRT cache drives

[John Pham]

Tampering w/ the partitions tables on the RAID volumes has the following
results:

With Parted on accelerated disk volume:
"Fixing" backup GPT not end of disk warning with parted : fail to boot Windows
"Fixing" warning that GPT is not using all space : fail to boot Windows

With Parted on SSD data disk volume:
"Fixing" backup GPT not end of disk with parted : boots
"Fixing" warning that GPT is not using all space : boots

with Gdisk on accelerated disk volume: 
Saving to accelerated volume while ignoring backup gpt not end of disk warning with parted: boots

Mounting  accelerated windows partition read-only works, as one would
expect since the drive is mounted in "enhanced" mode aka writethrough.
Comment earlier about it being fragile when mounted once was due to
running the above "fix" at the same time, although mounting it RW is
probably not a good idea due to cache consistency.

Haven't tried modifying partition tables directly w/o the raid layer,

If it fails to boot, going to the option rom and disabling acceleration
will allow booting, and reenabling from Windows still works. It'll cause
the warnings to show up in gpart/parted again though.

Haven't seen what happens if the accelerated drive is in
writeback/"maximum" mode and synced using the option ROM.

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https://bugs.launchpad.net/bugs/1251881

Title:
  dmraid-activate does not work on SRT cache drives

Status in “dmraid” package in Ubuntu:
  Incomplete

Bug description:
  Intel Smart Response creates a 1 drive "RAID0" on the cache drive, and
  puts the SSD data partitions on top. It also converts the accelerated
  drive to a 1-drive RAID0.

  The dmraid-activate script assumes all RAID0 instances  must have at
  least 2 drives, and fails to activate without printing any error
  messages, assuming drives are still coming online. This is
  particularly problematic in a dual-boot situation where Windows
  configures the SSD as cache with Intel SRT.

  Attached is a patch to fix this.

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