[Info-vax] RAID vs. MOUNT/BIND

[Forster, Michael]

I loved RAID 0+1 in the HSG80 days and pre-intelligent array days.

Michael

On Nov 23, 2010, at 2:35 PM, "Ken Fairfield" <ken.fairfield at gmail.com> wrote:

> On Nov 23, 11:25 am, Rob Brown <mylastn... at gmcl.com> wrote:
>> On Tue, 23 Nov 2010 at 09:15 -0800, Keith Lewis wrote:
>>> ... RAID 5 should theoretically give you both performance and
>>> redundancy.
>> 
>> RAID 5 gives redundancy, no argument there.
>> 
>> RAID 5 gives good read performance, but its write performance is not
>> as good.  Each logical write becomes 4 I/O: 2 reads and 2 writes.
>> 
>> If all of the extra I/O is hidden in hardware with deep caches, then
>> it may not be noticeable.  Or if you don't do so many writes, you may
>> not be bothered by poor write performance.
>> 
>> Or at least, that is the way it seems to me.
>> 
>> PS:  *Is* there a host-based RAID (other than 1 and 0) for VMS?
> 
> Yes, there *is* host-based raid for VMS.  In fact, I think
> that's it's product name. :-)
> 
> We used it when I was at my former employer.  It's
> pretty tightly integrated, and depends upon, host
> based volume shadowing.  My recollection is that
> you have only the single choice of RAID 0+1, i.e.,
> striped shadow sets.
> 
> It worked well, but could be tedious to set up
> initially.   A failed shadow set member was
> handled pretty much in the usual way, but ISTR
> the product be "happiest" if you used the RAID
> commands  to add a 3rd member to copy and
> to subsequently drop a failing member, etc.
> 
> I don't recall having any failures with the product...
> 
>   -Ken
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