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January 09, 2007


Nigel Poulton

Hi Chuck,

Thats a really insightful and interesting look into how EMC have approached this. Thanks for taking the time to share it.

Ive mentioned it over at rupturedmonkey on my most recent post.


PS. I'm a little unclear where the name rupturedmonkey came from but it was previously a security related website before Snig, the current owner, took it over and changed it to a storage website. Its not actually my site, Im just one of 3 guys who current blog there.


Thanks for the overview on how EMC² approaches solving problems. The term "marketing feature" has me puzzled though. Was RAID-S a marketing feature? Or was RAID-5 a marketing feature until you guys adopted it on the DMX?

The name Ruptured Monkey comes from the old saying "getting the monkey off my back". We just decided to rupture the monkey instead of being nice to the monkey. ;) It's all about helping others solve problems.

Chuck Hollis

Hi Snig

I'm going way back in history here, but I think the reason they called it "RAID S" rather than "RAID 5" is that the early Symmetrix implementation didn't have distributed parity between the participating logical volumes.

Unlike RAID 5, RAID S had a dedicated parity volume. Since it behaved differently than RAID 5, I think the logic was to call it something slightly different.

If you are trying to extend the statement I made about RAID 6 to RAID 5, I don't think it applies.

Let me take it in the other direction: if protecting against one disk failure (RAID 5) is good, and protecting against two simultaneous disk failures (RAID 6) is good, then -- by deduction -- protecting against three simultaneous disk failures (RAID X?) is good. And four disk failures, and so on.

Now, most people would reject the statement above, right?

Clearly, there are decreasing returns for the costs associated with additional protection. And the hard data we saw between RAID 5 and RAID 6 made us think about the problem differently.

Whether you agree with the thinking or not, I always think it's useful to share the logic that went into the decision.

Thanks for the comment!

Chuck Hollis

Quick update --

Just recently, EMC announced RAID 6 for the DMX platform. I'm sure at some point we'll see it for CLARiiON as well.

Thanks, all.

Bill Nicholls

Chuck, I owe you a big vote of thanks. Here's the story:

A week ago, one of my raid1 arrays went south and upon reconnection, updated from the offline drive, wiping a weeks worth of data off the good drive. :-{{

So I was busy investigating Raid5 or 6 for myself when I ran across your blog article. Hit the nail on the head, it did! I sat down and thought thru the whole process and here's what I found.

Primary cause: While I had the system open for swapping out a dead DVD, I brushed against one of the signal cables and dislodged it. The SATA connector had worn loose in just a few plugs.

I missed the 'array failure' warning until I rebooted, then went in and replugged the connector, not noticing how loose it had been. During the reboot I picked the default drive to rebuild from, which was wrong.

Net - one hardware failure, one cockpit error yields lost files. The disks were fine. Raid5 or 6 would have made no difference.

So, I am replacing the cheap SATA cables with ones that have snap clips. At $2 each, cheap insurance. Added a note to self - Pay Attention on Rebuilds!

Thanks a bunch,

Josh Savage

> First the Symmetrix team announced shipped RAID 6,
> and recently the CLARiiON team did the same.

So what's changed? 18 months ago, RAID-6 was irrelevant and now it's shipping in virtually all EMC products.

Seems like there are three possibilities:

1. The data suddenly changed in favor of RAID-6 (doubtful), or
2. You suddenly realized your analysis, though genuine, was faulty, or
3. Customer and competitive pressures trumped your "data", and you realized your "data-based" approach really wasn't the best way to make product feature decisions.

...or possibly some combination of the above. What's ironic is that behind closed doors, I'll bet you were reading the riot act to EMC engineers for not investing in this technology sooner ;-).

Any of the above true?

Chuck Hollis

None of the above.

For both platforms, there was a pareto regarding the most important challenges to go address first. Once the more important ones were solved, the team kept working down the list. And eventually got to RAID 6.

Just like the post says ...

At the time this post was written, certain vendors were making rather reckless statements regarding the superiority of RAID 6, and the inadequacy of RAID 5.

We believed at the time -- and still do -- that there's far more to end-to-end availability than just the choice of RAID.

Except that now that particular RAID 6 promoting vendor is now shipping RAID 5 VTLs .... !!


"So the EMC team made a rational decision – why don’t we focus our efforts on the things that actually cause customer problems, rather than marketing features that may or may not make an impact?

The counterargument was “hey, everyone else will have this feature, so we’ll be at a competitive disadvantage”. "

That is such a lame excuse for a supposed storage leader to leave out a feature that gets used quite a bit.

Chuck Hollis

Hi Mark -- the post you're commenting on is quite old, did you realize this?

You're entitled to your opinions regarding "lame excuses" from storage leaders.

Frankly, I think yours is a pretty weak comment, compared to some of the other more insightful ones we've seen here.

Thanks anyway ...

The comments to this entry are closed.

Chuck Hollis

  • Chuck Hollis
    SVP, Oracle Converged Infrastructure Systems

    Chuck now works for Oracle, and is now deeply embroiled in IT infrastructure.

    Previously, he was with VMware for 2 years, and EMC for 18 years before that, most of them great.

    He enjoys speaking to customer and industry audiences about a variety of technology topics, and -- of course -- enjoys blogging.

    Chuck lives in Vero Beach, FL with his wife and four dogs when he's not traveling. In his spare time, Chuck is working on his second career as an aging rock musician.

    Warning: do not ever buy him a drink when there is a piano nearby.

    Note: these are my personal views, and aren't reviewed or approved by my employer.
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