A-Team_Digital_Solutions/android_kernel_motorola_sm6375
Watch
2
0
Fork
You've already forked android_kernel_motorola_sm6375
 0
mirror of https://github.com/BobTheBlinker/android_kernel_motorola_sm6375.git synced 2026-10-29 03:01:39 -04:00
Code Issues Projects Releases Packages Wiki Activity

raid5-ppl: PPL support for disks with write-back cache enabled

Browse source 
In order to provide data consistency with PPL for disks with write-back
cache enabled all data has to be flushed to disks before next PPL
entry. The disks to be flushed are marked in the bitmap. It's modified
under a mutex and it's only read after PPL io unit is submitted.

A limitation of 64 disks in the array has been introduced to keep data
structures and implementation simple. RAID5 arrays with so many disks are
not likely due to high risk of multiple disks failure. Such restriction
should not be a real life limitation.

With write-back cache disabled next PPL entry is submitted when data write
for current one completes. Data flush defers next log submission so trigger
it when there are no stripes for handling found.

As PPL assures all data is flushed to disk at request completion, just
acknowledge flush request when PPL is enabled.

Signed-off-by: Tomasz Majchrzak <[email protected]>
Signed-off-by: Shaohua Li <[email protected]>
This commit is contained in:
Tomasz Majchrzak 2017-12-27 10:31:40 +01:00 • committed by Shaohua Li
commit 1532d9e87e
7 changed files with 195 additions and 25 deletions
Download patch file Download diff file Expand all files Collapse all files

7
Documentation/md/raid5-ppl.txt
View file

@ -39,6 +39,7 @@ case the behavior is the same as in plain raid5.
PPL is available for md version-1 metadata and external (specifically IMSM)
metadata arrays. It can be enabled using mdadm option --consistency-policy=ppl.
Currently, volatile write-back cache should be disabled on all member drives
when using PPL. Otherwise it cannot guarantee consistency in case of power
failure.
There is a limitation of maximum 64 disks in the array for PPL. It allows to
keep data structures and implementation simple. RAID5 arrays with so many disks
are not likely due to high risk of multiple disks failure. Such restriction
should not be a real life limitation.