🚀 go-pugleaf

In article <DDEuFG.2LJ@ftel.co.uk>, Ian G Batten <I.G.Batten@ftel.co.uk> wrote:
>In article <40sv62$nj8@sv01a.cis.squared.com>,
>Tony Gast <cis115@ws001a.cis.squared.com> wrote:
>> In article <40qs2d$5o9@news.cloud9.net>, tls@cloud9.net (Thor Lancelot Simon) writes:
>> |> 
>> |> Heavens, no.  Auspex does a perfectly good job of selling their fileservers
>> |> themselves.  Just for reference, do you know what an Auspex is?  They're 
>> |> specialized network file servers which can cost millions of dollars.  They
>> |> also happen to use a correct RAID implementation which does write caching 
>> |> without running the risk of losing the whole filesystem.
>> |> 
>> 
>> I recall seeing Auspex advertised.  This sounds even more costly to have
>> such a specialized machine, but I am sure there are companies that need
>> exactly this sort of dedicated device.
>
>Like us, for example.  What I can't understand from what tls is saying
>is why an NVRAM-equipped SCSI controller isn't sufficient to guard
>against the scenario he describes (power failure with writes uncommitted
>to disk)?  We have a Write Accelerator in our Auspex, and I think I
>understand how it works.  Why is an NVRAM+disk combination any less
>secure than a disk alone?  Why does the code at the host end of the SCSI
>chain need to know that the far end has a cache with NVRAM?  Surely,
>provided any acknowledged write down the SCSI chain can be followed
>(possibly after a power fail) with a correct read from the same location
>on disk, everyone is happy?

Yes, of course it is.  That's why an Auspex *works*.  Auspex doesn't ever 
store uncommitted writes in *volatile* RAM unless the filesystem knows about
it -- unless it doesn't think those writes are committed, essentially.  

The default configuration of the StorComp RAID 7 box *does* store 
uncommitted writes in volatile RAM -- and it lies to the host it's 
attached to about it.  That's why it performs better than anyone else's 
RAID 4 on writes.  That is, in fact, the _only difference_ between it and 
anyone else's RAID 4, essentially.

See why it's a bad product, now?  They did just introduce optional NVRAM, 
but they hardly advertise that you might lose your filesystem metadata if 
you don't buy it.
-- 
Thor Lancelot Simon                                               tls@cloud9.net

Somewhere they're meeting on a pinhead, calling you an angel.