-----Original Message----- From: Keld Jørn Simonsen [mailto:keld@xxxxxxxx] Sent: Wednesday, April 23, 2008 1:47 PM To: David Lethe Cc: Ty! Boyack; linux-raid@xxxxxxxxxxxxxxx Subject: Re: managing raid on Linux On Wed, Apr 23, 2008 at 01:17:19PM -0500, David Lethe wrote: > > Well, this is the norm. While some APIs are well done, the other > extreme is that vendor xyz farmed out the API/drivers to another > company, and the hardware vendor doesn't have the resources, knowledge > or experience to provide the information necessary to bring a 3rd-party > management tool to market. I will certainly not reveal anything about > the companies that did farm out the software/firmware to 3rd parties, > and will not tell you if their names were mentioned in this post. > Suffice to say that this is a real problem with SOME controllers that > people reading this post have installed in their computers. > > - The economics of developing support for a particular controller is a > severe constraint. Consider the reasons above, and then add simple > equipment costs for development/testing, and then support. I'm not > going to add support for product xyz unless I know it will be > profitable, and even a hundred end-user requests won't begin to pay for > such an effort. > > - I for one certainly can't keep up with all the new things coming > out, so we choose our battles wisely based on the market opportunity, > longevity of the controller platform, safety/robustness of the API, and > development/ongoing support expense. > > So there are the reasons why the OP can't find anything that supports > everything he has. David, thanks for your explanation of the current situation for making an übermanageri for HW RAID. The prospects seem dark indeed. Are there then more future in doing it the SW RAID way, as the Linux Kernel stuff we are discussion here on this mailing list? Are there chances that this work om Linux RAID can match or be better on the issues of performance, raid personality flavours and management, compared to the best of the HW RAID manufacturers? Best regards keld ============================================ Keld - Well, I don't want to insult the outstanding work product that everybody has put forth in LINUX, md/raid ... but from my perspective coming from the hardware RAID world, and software appliance perspective, then it is a mixed bag. Pure software RAID, as designed in the LINUX kernel is superior in terms of potential performance to many internal RAID controllers. I break NDAs if I give specific reasons to explain this, but here is one reason that is inherent to the differences in architectures. Consider that the fastest I/O is the one that doesn't have to be performed, and software-kernel-based RAID has the luxury of not having to perform an I/O if it knows the data exists somewhere in CPU cache, L1/L2 cache, or even RAM. Here I can "satisfy" an I/O in nanoseconds. If I have to get an I/O from a card on a BUS, or external storage, then it will take milliseconds, even if solid-state disk is attached. Bus/protocol limitations for one, plus the speed of light is just too darned slow. But Hardware RAID has other things going for it in terms of snapshot, compression, and even performance depending on the I/O requirements. You can offload calculations and smooth and balance I/O easily in some configs. No architecture is "best" in all cases, even if price was taken out of the picture. In terms of reliability, availability, and clustering capability, then LINUX need a major redesign in both architecture & design philosophy. Not trying to shove zfs down anybody's throat, but read up on the specs and architecture and features and then decide for yourself. There are GPL reasons why zfs isn't available today in the kernel, and philosophical/legal/logistical (but non-technical) reasons holding software-based RAID in LINUX back. As for management, Sorry, the economics don't make it possible for LINUX to compete, except in point solutions .. not when you have EMC, CA, HP, IBM, MSFT, and all the rest spending billions of dollars on programmers writing management software. David @ SANtools ^ com -- 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
