Is Write back cache enabled on physical disks of Perc 6/i ?

Dushyanth dushyanth at gmail.com
Thu Mar 26 10:15:33 CDT 2009


Hi,

Christian Rishøj <christian <at> jetment.com> writes:
> 
> 
> On 26 Mar 2009, at 11:32, Dushyanth wrote:
> 
> >> Any pointers/suggestions would be of great help.
> >
> > Does anyone know if write back cache is enabled on the physical  
> > disks of
> > Perc 6/I controllers ?
> 
> Our server came from Dell with disk caches disabled. We saw a small  
> performance gain by enabling it ourselves.
> 
> You can inspect the configuration with omreport. E.g.:
> 
> $ sudo omreport storage vdisk
> List of Virtual Disks in the System

The virtual disk status (raid array) shows write back status. Mine does too.
Each hard disk in that raid array also has cache (disk cache). The physical
disks status of the virtual disk does not confirm whether those disk caches are
disabled (check below). 

# omreport storage pdisk vdisk=0 controller=0
List of Physical Disks belonging to Virtual Disk 0

Controller PERC 5/i Integrated (Embedded)
ID                        : 1:0:8
Status                    : Ok
Name                      : Physical Disk 1:0:8
State                     : Online
Failure Predicted         : No
Progress                  : Not Applicable
Type                      : SAS
Capacity                  : 67.75 GB (72746008576 bytes)
Used RAID Disk Space      : 67.75 GB (72746008576 bytes)
Available RAID Disk Space : 0.00 GB (0 bytes)
Hot Spare                 : No
Vendor ID                 : DELL
Product ID                : ST373455SS
Revision                  : S515
Serial No.                : 3LQ1WD3C
Negotiated Speed          : Not Available
Capable Speed             : Not Available
Manufacture Day           : 07
Manufacture Week          : 41
Manufacture Year          : 2005
SAS Address               : 5000C500070697FD

Enabling virtual disk write back cache is not safe without a battery backup on
the PERC controller. Again, i don't know whether these PERC controllers come
with battery backup by default. omreport doesn't show any such state for the
controller i,e whether battery is installed or not for the controller.

TIA
Dushyanth





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