Write caching allegedly causing data damage

Posted on 2009-04-22
Last Modified: 2012-05-06
We have a customer who run a third party database application related to their business of property rentalls.
On the advice of the developer of the software they run a twice daily data integrity check due to frequent data damage. At least twice a week the checker reports that the data is damaged and must be restored from backup resulting in the loss of half a days work.
Following a list of prerequisites set out by the developer we have extensively reconfigured the system with memory upgrades, power management settings, replacement of unsupported NIC chipsets and even recabling of the office.
The application has a diagnostics utility which lists these prerequisites one being write Caching being enabled.
They have a Dell PE840 with a Perc5/i raid controller in a raid 5 config and Dell PCs (optiplex and Dimension) all running xpsp2.
Dell tech support have confirmed that write caching cannot be completely disabled on the server with this Raid config but that on the PCs write caching is a software setting only.
We have disabled write caching in windows under the policy tab on the properties of each disk yet the Diags utility still reports that write caching is enabled.
Because of this the developer is refusing to look any further.
Is there anywhere else we can look or is this just the way it is (as we believe) with modern systems??
The server runs server 2003 SBS and all that goes with it without any problem.
We would love the cutomer to ditch this system and use a more robust application.
Question by:omnisys
    LVL 55

    Expert Comment

    Make sure you have battery backup units on all the RAID controllers. The diags are probably not suitable to check the write cache status of a RAID card, for example the OS may tell the controller to disable caching but the controller is likely to ignore th command because there is no need to disable it as long as it is backed up by a battery.

    Author Comment

    Thanks for your input andyalder. I suppose what I'm actually asking is can we prove to these people that write caching is disabled as much as it possibly can be so they stop using this as the reason for the data corruption.
    LVL 55

    Accepted Solution

    I think you'll have to get a statement out of Dell technical support saying that write caching cannot possibly cause data corruption except in the case of power loss and even with power loss cannot cause data corruption until the cache battery goes flat.

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