== Always Write Back is good, Write Through is bad ==

I'm not even sure what that means but I found out when setting up the LSI RAIDs on
vso04 and vso05. Here are the notes :

{{{

# /opt/MegaRAID/storcli/storcli64 /c0 show

This showed, in part :

VD LIST :
=======

----------------------------------------------------------------
DG/VD TYPE  State Access Consist Cache Cac sCC       Size Name  
----------------------------------------------------------------
1/238 RAID6 Optl  RW     Yes     RWTD  -   ON  127.329 TB RAID6 
0/239 RAID1 Optl  RW     Yes     RWTD  -   ON    1.745 TB RAID1 
----------------------------------------------------------------

That WT means "Write Through" - this is apparently bad and wrong.
We want "Always Write Back" instead. So do this :

# /opt/MegaRAID/storcli/storcli64 /c0/v238 set wrcache=awb
# /opt/MegaRAID/storcli/storcli64 /c0/v239 set wrcache=awb

Which looks like this when executed :

# /opt/MegaRAID/storcli/storcli64 /c0/v238 set wrcache=awb
CLI Version = 007.2309.0000.0000 Sep 16, 2022
Operating system = Linux 4.18.0-513.9.1.el8_9.x86_64
Controller = 0
Status = Success
Description = None

Detailed Status :
===============

----------------------------------------
 VD Property Value Status  ErrCd ErrMsg 
----------------------------------------
238 wrCache  AWB   Success     0 -      
----------------------------------------

# /opt/MegaRAID/storcli/storcli64 /c0/v239 set wrcache=awb
CLI Version = 007.2309.0000.0000 Sep 16, 2022
Operating system = Linux 4.18.0-513.9.1.el8_9.x86_64
Controller = 0
Status = Success
Description = None

Detailed Status :
===============

----------------------------------------
 VD Property Value Status  ErrCd ErrMsg 
----------------------------------------
239 wrCache  AWB   Success     0 -      
----------------------------------------


The "show" command :
# /opt/MegaRAID/storcli/storcli64 /c0 show
now looks, in part, like this :

VD LIST :
=======

----------------------------------------------------------------
DG/VD TYPE  State Access Consist Cache Cac sCC       Size Name  
----------------------------------------------------------------
1/238 RAID6 Optl  RW     Yes     RAWBD -   ON  127.329 TB RAID6 
0/239 RAID1 Optl  RW     Yes     RAWBD -   ON    1.745 TB RAID1 
----------------------------------------------------------------

This is apparently a vast improvement.

}}}