Disk controller write caching

Disk controller write caching

Post by Mike Storm » Tue, 17 Feb 1998 04:00:00



Microsoft documentation for Error 625 (which I've been getting) says to make
sure disk controller write caching is not enabled. Is this common knowledge
and practice, to disable disk controller write caching on SQL servers? Or is
it only a "possible" cause for some types of data corruption--to be tried
only if other solutions fail?

TIA

 
 
 

Disk controller write caching

Post by Stuart Minga » Wed, 18 Feb 1998 04:00:00


depends what controller it is really, I believe that Compaq supply the
only 'approved' write cache controller

Stu


> Microsoft documentation for Error 625 (which I've been getting) says to make
> sure disk controller write caching is not enabled. Is this common knowledge
> and practice, to disable disk controller write caching on SQL servers? Or is
> it only a "possible" cause for some types of data corruption--to be tried
> only if other solutions fail?

> TIA



 
 
 

Disk controller write caching

Post by Neil Pik » Wed, 18 Feb 1998 04:00:00


Mike,

 Check with your raid controller vendor - as long as it doesn't have
any bugs then you should be ok.  Obviously don't run without battery
backup.

 Neil Pike MVP/MCSE
 Protech Computing Ltd

 
 
 

Disk controller write caching

Post by Roy Harv » Wed, 18 Feb 1998 04:00:00


Neil,

Quote:>Obviously don't run without battery
>backup.

Just to emphasize that this is NOT just plugging the server into a
UPS, this means batteries mounted on the disk controller itself to
keep the write cache alive.

Roy

 
 
 

Disk controller write caching

Post by Neil Pik » Wed, 18 Feb 1998 04:00:00


Correct - I'd have the UPS/APS as well though.

 Neil Pike MVP/MCSE
 Protech Computing Ltd

 
 
 

Disk controller write caching

Post by Jamie Jackso » Thu, 05 Mar 1998 04:00:00


What is the purpose of this?  To get extended battery time beyond what the
UPS provides, or to cover any possible lag time between socket power cutoff
& UPS power starting, or something else?  How would "batteries be mounted on
the disk controller itself"?

Quote:>>Obviously don't run without battery
>>backup.

>Just to emphasize that this is NOT just plugging the server into a
>UPS, this means batteries mounted on the disk controller itself to
>keep the write cache alive.

>Roy

 
 
 

Disk controller write caching

Post by Richard Waymir » Thu, 05 Mar 1998 04:00:00


On the compaq smart-array 2 controllers there are what look like "AA"
batteries on the controller card to protect the write cache.

--
Richard Waymire, MCT, MCSE+Internet, MCSD, MVP (SQLServer)
Senior Principal Instructor/Consultant, ARIS Corp.
President, Pacific NW SQLServer Users Group (http://www.pnwssug.org)
Visit us at http://www.aris.com


>What is the purpose of this?  To get extended battery time beyond what the
>UPS provides, or to cover any possible lag time between socket power cutoff
>& UPS power starting, or something else?  How would "batteries be mounted
on
>the disk controller itself"?

>>>Obviously don't run without battery
>>>backup.

>>Just to emphasize that this is NOT just plugging the server into a
>>UPS, this means batteries mounted on the disk controller itself to
>>keep the write cache alive.

>>Roy

 
 
 

Disk controller write caching

Post by Roy Harv » Thu, 05 Mar 1998 04:00:00


Jamie,

A UPS can carry you through a power outage - for a while - but it
cannot handle someone removing the power cord or hitting the OFF
switch.  The batteries on the controller keep the memory on the
controller alive for a few days so that when power is restored the
controller can write any unwritten part of the write cache.  Without
such an arrangement you are heading for database corruption.

Roy


>What is the purpose of this?  To get extended battery time beyond what the
>UPS provides, or to cover any possible lag time between socket power cutoff
>& UPS power starting, or something else?  How would "batteries be mounted on
>the disk controller itself"?

>>>Obviously don't run without battery
>>>backup.

>>Just to emphasize that this is NOT just plugging the server into a
>>UPS, this means batteries mounted on the disk controller itself to
>>keep the write cache alive.

>>Roy

 
 
 

Disk controller write caching

Post by Tibor Karasz » Thu, 05 Mar 1998 04:00:00


One additional thing to consider (?):

Hw crash of the disk controller. Battery backup wouldn't help here.

I've heard that DEC (on some controller) has an option where you use a cord
between the failed controller and a new one to transfer the cache (wouldn't
help if memory on controller crashed)...
--

MCSE, MCSD, MCT, SQL Server MVP
Cornerstone Sweden AB



Quote:> Jamie,

> A UPS can carry you through a power outage - for a while - but it
> cannot handle someone removing the power cord or hitting the OFF
> switch.  The batteries on the controller keep the memory on the
> controller alive for a few days so that when power is restored the
> controller can write any unwritten part of the write cache.  Without
> such an arrangement you are heading for database corruption.

> Roy

 
 
 

Disk controller write caching

Post by Roy Harv » Fri, 06 Mar 1998 04:00:00


Tibor,

Quote:>One additional thing to consider (?):

>Hw crash of the disk controller. Battery backup wouldn't help here.

>I've heard that DEC (on some controller) has an option where you use a cord
>between the failed controller and a new one to transfer the cache (wouldn't
>help if memory on controller crashed)...

Compaq places the memory and batteries on a daughter card that is
transferable to a replacement controller card.

Roy

 
 
 

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should ensure that all data caching is properly handled. In many situations,
this means you must disable the write caching of the disk drive."

Thanks.

Mike

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