CPU utilization is certainly one of the metrics we try our best to optimize for. When one drops CPU utilization on a server, one can opt for a cooler running or cheaper main processor. The XOR engine, DMA engines and Cache are the three feature assists that allow a less meaty (read, lower cost, lower heat) processor on the HW Raid cards and yet offer some added performance or cost advantages. The more appropriate processing power is necessary when trying to keep the heat down in a 1U enclosure for instance. Keeping the number of interrupts down to the main CPU, especially if it is not a class of CPU designed for I/O throughput such as the x86 designs, will keep the context switching and CPU utilization to a minimum. OS independent Boot ability, Configuration tools, Install ability, Boot Redundancy, Hardware based Hot Swapping and years of Intellectual Property and Experience have to add up to something ;-> It is extremely difficult to qualify a product and tidily placing `ownership' of RAID problems into one engineering entity with strict revision and quality control turns into one main reasons HW RAID still represents a viable solution in the enterprise space. EMD was born out of the needs of the OEM clashing with the needs of the many ;-/ Attempts have been made to use lower cost neutered HW (ie no hot swap for instance) or SW solutions in the Enterprise space, the results have been both costly and devastating. Linux stands in the Enterprise, Desktop and Embedded space; it behoves the engineer to take each space's needs on their own merits. For instance, I probably would not use a HW RAID controller in an embedded application unless I could measure cost savings or performance improvements on the Host Processor that offset the cost of the added HW. But in the Enterprise space I would require one of the HW features and it would be a no brainer. There are no simple answers regardless. Sincerely -- Mark Salyzyn -----Original Message----- From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Ricky Beam Sent: Friday, May 21, 2004 11:57 AM To: Ben Edwards Cc: Linux RAID List Subject: Re: Hardware versus Software On Wed, 19 May 2004, Ben Edwards wrote: >... I would be very suprised if software raid was >faster and if it is I wold think the card is either broke or rubish Negative. HW RAID cards may have specialized hardware for doing XOR calculations. However, no raid card currently on the market has a 3.2GHz xeon at it's core. Most are ARM (up to 750MHz?) or i960 (up to 66MHz) based. The system CPU can certainly out perform the tiny processors on the raid card. Of course, if it's doing raid calculations, it's not do general computational work which is one reason to use hw raids. --Ricky - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
