Re: sd incorrectly reports write cache disabled on cache-capable drives/controllers

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Fri, 2008-01-25 at 22:28 +0100, Halim Issa wrote:
> Thank you so much for the quick reply - I risk asking one follow-up question.
> 
> On Friday 25 January 2008 22:15:20 James Bottomley wrote:
> > The "cache" hear would be referring to the RAID controller cache, not
> > the disk cache.  Likewise DPO and FUA refer to what the RAID controller
> > can support, not the disk.
> 
> Would it be safe to assume that the problem thus lies within the mptfusion 
> driver, since a) the LSI Logic controller in question does indeed have 
> hardware cache capabilities; and b) an older kernel version as well as 
> Windows Server, correctly loads with the correct cache parameters at boot?

I don't think it would be correct to assume that there actually is a
problem.  Most RAID controllers habitually lie about having a cache in
their INQUIRY strings because they don't want to deal with the kernel
sending SYNCHRONIZE_CACHE commands down.

Just because the inquiry strings say it doesn't have a cache doesn't
really mean it's not using one but not telling anyone.

James