[CentOS] CentOS 5.5 does not recognise SAS drives with LSI 1068E Controller
John R Pierce
pierce at hogranch.com
Thu Mar 10 19:50:51 UTC 2011
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.
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