Thanks for the detailed response - further questions inline...
Christopher George wrote:
Excellent questions!
I see the PCI card has an external power connector - can you explain
how/why that's required, as opposed to using an on card battery or
similar.
DDRdrive X1 ZIL functionality is best served with an external attached UPS,
this allows the X1 to perform as a non-volatile storage device without specific
user configuration or unique operation. An often overlooked aspect of batteries
(irrespective of technology or internal/external) is their limited lifetime and
varying degrees of maintenance and oversight required. For example, a
lithium (Li-Ion) battery supply, as used by older NVRAM products and not the
X1, does have the minimum required energy density for an internal solution.
But has a fatal flaw for enterprise applications - an ignition mode failure
possibility. Google "lithium battery fire". Such an instance, even if rare,
would be catastrophic not only to the on-card data but the host server and so
on... Supercapacitors are another alternative which thankfully do not share
the ignition mode failure mechanism of Li-Ion, but are hampered mainly by
cost with some longevity concerns which can be addressed. In the end, we
selected data integrity, cost, and serviceability as our top three priorities.
This led us to the industry standard external lead-acid battery as sold by APC.
Key benefits of the DDRdrive X1 power solution:
1) Data Integrity - Supports multiple back-to-back power failures, a single
DDRdrive X1 uses less than 5W when the host is powered down, even a
small UPS is over-provisioned and unlike an internal solution will not normally
require a lengthy recharge time prior to the next power incident. Optionally a
backup to NAND can be performed to remove the UPS duration as a factor.
2) Cost Effective / Flexible - The Smart-UPS SC 450VA (280 Watts) is an
excellent choice for most installations and retails for approximately $150.00.
Flexibility is in regard to UPS selection, as it can be right-sized (duration)
for
each individual application if needed.
3) Reliability / Maintenance - UPS front panel LED status for battery
replacement and audible alarms when battery is low or non-operational.
Industry standard battery form factor backed by APC the industry leading
manufacture of enterprise-class backup solutions.
OK, I take your point about battery fires, however we've been using
battery backed cards (of various types) in servers for a while now, and
I think you might have over over-emphasized those risks, when compared
to the operational complexity of maintaining a separate power circuit
for my PCI cards! But then, I haven't actually done the research on
battery reliability either. :-)
I'm not sure about others on the list, but I have a dislike of AC power
bricks in my racks. Sometimes they're unavoidable, but they're also
physically awkward - where do we put them? Using up space on a dedicated
shelf? Cable tied to the rack itself? Hidden under the floor?
Is the state of the power input exposed to software in some way? In
other terms, can I have a nagios check running on my server that
triggers an alert if the power cable accidentally gets pulled out?
What happens if the *host* power to the card fails?
Nothing, the DDRdrive X1's data integrity is guaranteed by the attached UPS.
OK, which means that the UPS must be separate to the UPS powering the
server then.
The 155mb rate for sustained writes is low for DDR ram?
The DRAM's value add is it's extremely low latency (even compared to NAND)
and other intrinsic properties such as longevity and reliability. The
read/write
sequential bandwidth is completely bound by the PCI Express interface.
Any plans on a pci-e multi-lane version then? All my servers are still
Gig-E, and I'm not likely to see more than 100MB/sec of NFS traffic,
however I'm sure there are plenty of NFS servers on 10G out there that
will see quite a bit more than 155MB/sec for moderate amounts of time. I
know we can put more than one of these cards in a server, but those
slots are often taken up with other things!
I look forward to these being available in Australia :-)
Thanks,
Tristan
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