[CentOS] Centos/Linux Disk Caching, might be OT in some ways

Ross Walker rswwalker at gmail.com
Fri Jan 29 00:08:00 UTC 2010


On Jan 28, 2010, at 6:58 PM, "nate" <centos at linuxpowered.net> wrote:

> Ross Walker wrote:
>
>> Even directio by itself won't do the trick, the OS needs to make sure
>> the disk drives empties it's write cache and currently barriers are
>> the only way to make sure of that.
>
> Well I guess by the same token nobody in their right mind
> would run an Oracle DB without a battery backed write cache :)

True, or at a minimum a UPS.

There are patches in the current kernel versions that add barrier  
support to LVM, but how long till they are backported to RHEL is  
anyone's guess.

There are concerns that everyone's currently fast performing LVM file  
systems will suddenly become doggish once barrier support is included  
and in some cases it will be true. Using a separate SSD device as a  
journal can help in some cases.

-Ross



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