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. > What happens if the *host* power to the card fails? Nothing, the DDRdrive X1's data integrity is guaranteed by the attached UPS. > 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. > Is this because the backup to NAND is a constant thing, rather than only > at power fail? No, the backup to NAND is not continual. All Host IO is directed to DRAM for maximum performance while the NAND only provides an optional (user configured) backup/restore feature. Christopher George Founder/CTO www.ddrdrive.com -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
