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

[John Pham]

I forgot to clarify.  The problem the patch tries to solve is mounting
Linux partitions on drives that are on the cache drive or accelerated,  and
not acceleration on Linux. What ISRT does is make a single drive "RAID0"
container for the data portion of the SSD that doesn't contain the cache
and another for the drive being accelerated if it is not already in an
Intel RAID volume (haven't verified what happens if there is one already).
dmraid -a y currently mounts these, with the following caveats...

Data loss may happen if the Windows partitions from the accelerated
volumes/drives are even mounted once due to cache invalidation; possibly
another change to the script to remove device files belonging to Windows
accessible partitions generated by kpartx would be useful - this probably
needs to be done even if this change isn't applied due to the possibility
of accelerating multidrive volumes which would mount anyway and then break
currently. Data partitions on the SSD may be safe; I have not yet tried
this.

Mdadm detects unknown attributes and refuses to activate anything at all,
while dmraid allows this allowing access to Linux partitions, but with the
above risks.

If dmraid isn't activated I believe the underlying partitions are visible
and usable, albeit with RAID, but there might be data loss by modifying the
underlying partitions directly, or having gdisk/parted "fix" things. There
are some errors about gpt backup information even editing the RAID, but
having gdisk "fix" this on the SSD data seems to be okay. I'll need to
reverify this, and check for the accelerated volume and make sure it
doesn't break anything on either OS.
On Nov 16, 2013 11:00 PM, "Phillip Susi" <psusi at ubuntu.com> wrote:

> I don't see how this change will make it work.  The problem is not
> simply with dmraid-activate and the number of drives in the set, but the
> fact that dmraid and device-mapper do not know anything about the format
> of the intel cache system, so they can not use such a drive.
>
>
> ** Changed in: dmraid (Ubuntu)
>        Status: New => Incomplete
>
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> https://bugs.launchpad.net/bugs/1251881
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> Title:
>   dmraid-activate does not work on SRT cache drives
>
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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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