Public bug reported:

On a Bionic server (Cisco UCS C240 M5) with a MegaRaid controller (Cisco 12G 
Modular Raid Controller UCSC-RAID-M5), I can observe very slow writes on the 
RAID 10 device that was created.
A simple test:
dd if=/dev/zero of=out bs=1M count=100
Outputs a 35MB/s speed.

The RAID 10 is composed of 4 HDDs (TOSH MG04SCA60EA T0A0CAF8YC 6TB) was 
configured with the default settings [0]:
Strip size: 64K
Access Policy: RW
Read Policy: Normal
Write Policy: Writethrough
IO Policy: Direct
Disable BGI: No

uname -a
4.15.0-48-generic #51-Ubuntu SMP

[0]
https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/c/sw/raid/configuration/guide/RAID_GUIDE/MegaRAID.html

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete


** Tags: bionic

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https://bugs.launchpad.net/bugs/1828351

Title:
  RAID 10 with MegaRaid controller gives poor write performance

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  On a Bionic server (Cisco UCS C240 M5) with a MegaRaid controller (Cisco 12G 
Modular Raid Controller UCSC-RAID-M5), I can observe very slow writes on the 
RAID 10 device that was created.
  A simple test:
  dd if=/dev/zero of=out bs=1M count=100
  Outputs a 35MB/s speed.

  The RAID 10 is composed of 4 HDDs (TOSH MG04SCA60EA T0A0CAF8YC 6TB) was 
configured with the default settings [0]:
  Strip size: 64K
  Access Policy: RW
  Read Policy: Normal
  Write Policy: Writethrough
  IO Policy: Direct
  Disable BGI: No

  uname -a
  4.15.0-48-generic #51-Ubuntu SMP

  [0]
  
https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/c/sw/raid/configuration/guide/RAID_GUIDE/MegaRAID.html

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