Re: external storage and commit?

From: Sean M <smckeownNO_at_BACKSIESearthlink.net>
Date: Mon, 15 Apr 2002 11:24:57 -0600
Message-ID: <3CBB0CE9.B6C0ABF8@BACKSIESearthlink.net>

Tim Smith wrote:
>
> Hi,
> For Direct Attached Storage I believe I am correct in saying that
> when a transaction is committed it is written to disk.
>
> For external storage, such as an IBM ESS(Shark) am I correct in
> saying that a transactions may be written to the ESS cache and not
> written to disk?

I'm not explicitly familiar with ESS hardware, but from what I've read it works very much the same as other popular (i.e. EMC) disk subsystems. In which case, yes, this is correct.

> Would this mean a subsequent general power failure could cause
> transactions (otherwise supposed to be committed) to be lost?

No (again, assuming Shark works like the others, which it does according to http://www.storage.ibm.com/hardsoft/products/ess/essspec.htm), because the cache itself is NVRAM. A write to cache is as good as a write to disk.

Regards,
Sean Received on Mon Apr 15 2002 - 12:24:57 CDT