Perc 5/iR - Write Cache

Seaniboy

Seaniboy

Seaniboy

Associate
Joined
27 Dec 2007
Posts
241
One of the SBS servers i look after with the above SAS card is having some performance issues with it, in the end I tracked it down to massive disk write times (average 1000+!!!). I noticed the disk cache policy was disabled.

I have enabled this and it has immediately brought the disk write times down to a respectable average of 3 - 4.

Now if memory serves me right I am pretty sure that particular SAS controller does not have battery backup. Has anyone here in the past come across any major issues before doing the above? I.e corruption, major data lose etc...?
 
Seaniboy said:
One of the SBS servers i look after with the above SAS card is having some performance issues with it, in the end I tracked it down to massive disk write times (average 1000+!!!). I noticed the disk cache policy was disabled.

I have enabled this and it has immediately brought the disk write times down to a respectable average of 3 - 4.

Now if memory serves me right I am pretty sure that particular SAS controller does not have battery backup. Has anyone here in the past come across any major issues before doing the above? I.e corruption, major data lose etc...?
Click to expand...


Hi


You will not get any Issues not having battery backed Cache, as long as you dont have a power failure!.

say have 256MB write cache, this means that at anyone time there could be 256MB of data sat in the RAM on the PERC controller. The Controller will have informed you applications that the data has been written to disk (even though it has not 'actually' been). The Controller will then write this to disk at the best and most appropriate time.

If you where to have a power failure to the server for whatever reason (someone pulls a cable by accident!) that 256MB of data will be instantly lost forever. This is where you could / will get big issues, as when the server reboots your apps will be missing 256MB of data - not good.

The Battery will keep power to that RAM untill the server is rebooted and it can be comitted to disk correctly.


It is not wise to run without the battery unless you can ensure no power loss, ie a good UPS and no accidental power loss situations.

Hope this helps
 
Can you get a BBWC add-on module for the controller? I don't know the PERC cards very well but I know the lower end HP SmartArray can usually be upgraded with a simple clip-on board.
 
Hi. Do you have Dell Open Manage installed? If so this will allow you to check the battery status on the RAID card.
 
You must log in or register to reply here.
Back
Top Bottom