HDS TCO/ROI Guru starts Blogging

Today, I read in Hu Yoshida's blog entry that David Merrill has decided to join blogosphere community.

For last few years, I have extensively used ideas from his Storage ROI/TCO work in building business cases for storage technologies. Typically, vendor white papers have limited lifespan and focus on specific products. In my opinion, this is not the case with his work. With the longevity and usefulness of his ROI/TCO white papers, I sometime wonder how come he hasn't thought about writing a book on Economics of Storage.

If you are involved on business side of storage technologies, you may want to read his ROI/TCO work. It is time well wasted, comedy central style!

Welcome David, I am looking forward to reading your thoughts on storage economics. And considering how many HDS people are now blogging, may be you and Jeremiah want to collaborate on a case study for ROI of corporate blogs.

Double Disk Failure - Follow up

Yesterday, Dave wrote about double disk failure in his blog (See Expect Double Disk Failures with ATA Drives). I agree with Dave's comment "As drives grow, I suspect that it (double protecting RAID) will become a requirement even for Fibre Channel drives." In my opinion, as the rebuild time goes beyond 12 hours, it will become requirement for all drives.

Couple of weeks ago, I also wrote about double disk failure event I encountered (See Data loss risk during RAID rebuild). And my concerns about increased exposure to data loss as RAID rebuild time is getting longer with higher disk capacity in RAID groups (See Happy New Year & Food for Your Brain). I prefer to have a Plan B if the RAID5 rebuild time is going to exceed 6 to 8 hours.

In last couple of weeks, my readers and colleagues referred me to several good articles on RAID protection. Here are two that I found really interesting and useful.

Daniel Feenberg, Things we wish we'd known about NAS devices and Linux Raid

… the majority of single drive failures are followed by a second drive failure before redundancy is established.

The fault lies with the Linux md driver, which stops rebuilding parity after a drive failure at the first point it encounters a uncorrectable read error on the remaining "good" drives.

A single unreadable sector isn't unusual among the tens of millions of sectors on a modern drive. If the sector has never been written to, there is no occasion for the drive electronics or the OS to even know it is bad. If the OS tried to write to it, the drive would automatically remap the sector and no damage would be done - not even a log entry. But that one bad sector will render the entire array unrecoverable no matter where on the disk it is if one other drive has already been failed.

We don't know what the reconstruction policy is for other raid controllers, drivers or NAS devices. None of the boxes we bought acknowledged this "gotcha" but none promised to avoid it either.

K.K. Rao, James L. Hafner and Richard A. Golding, Reliability for Networked Storage Nodes (pdf)

By using drive bandwidth more efficiently through the use of larger rebuild block sizes, we see significant improvements in reliability. In fact, the rebuild block size is a controllable parameter with the most significant impact on reliability.

No right or wrong answers to EQ tests

Do you score high on EQ (Entrepreneurial Quotient) tests like the one
posted by Guy Kawasaki? The high score doesn't necessarily mean that you will make a better entrepreneur. But, you may have a future as a writer who may become successful writing business books.

I took Kawasaki's test but with a twist. I answered eleven questions based on what popular entrepreneurship culture preaches and eleven questions based on my actual experiences. I got three times as many wrong answers when I answered based on my experiences instead of what entrepreneurship books preach.

I used to be a typical engineering guy and had no background in business. So I read a lot of books on entrepreneurship, joined associations and attended events. And only thing I can say that the preachings of popular entrepreneurship culture will not make you successful. The key to success is flexibility and considering all available alternatives.

In my opinion, there is no right or wrong answer to EQ tests, all answers are valid alternatives until one works for you.