[CentOS] CentOS 5.5 does not recognise SAS drives with LSI 1068E Controller

Thu Mar 10 19:50:51 UTC 2011
John R Pierce <pierce at hogranch.com>

On 03/10/11 11:36 AM, Les Mikesell wrote:
> Sure, UPS's fail, plugs get pulled, etc., but the cards and internal
> batteries most likely have their own failure modes.  Or the whole box
> can fry at once.  Did you have any way to tell if your battery-backed
> saved any data as the disks lost power or did the filesystems just back
> out the incomplete writes anyway?

battery backed writeback caches on raid controllers flush any pending 
data to the disks when power is restored.   if for some reason they 
can't, they flag an error

when an application (such as database server) or file system issues a 
fdatasync or fsync, it expects that when that operation returns success, 
all data has been committed to non-volatile storage.    BBWC exist to 
speed up that critical operation, as actualy committing data to disk is 
slow and expensive.     This is of particular importance to a 
transactional database server, each COMMIT;  has to be committed to disk.

I am intentionally sidestepping the issue of cheap desktop grade storage 
that ignores buffer flush commands as these really aren't suitable for 
transactional database servers unless your data just isn't that 
important.   IDE and SATA stuff has always been 'soft' on this, while 
SCSI, FC, and SAS drives are much more consistent.