Comments on: Of EMC, RAID 6, mud and Dragons

By: infos über Raid Systeme

infos über Raid Systeme — Sun, 04 Dec 2011 01:01:23 +0000

infos über Raid Systeme…

[...]Of EMC, RAID 6, mud and Dragons – Technical Deep Dive[...]…

By: Wayne

Wayne — Sat, 11 Aug 2007 02:15:01 +0000

EMC now supports RAID6 with FLARE release 26: http://www.emc.com/techlib/abstract.jsp?id=1878&c=US&l=en

By: richard

richard — Fri, 19 Jan 2007 04:51:30 +0000

I guess that HDS can do very little when it happens … unless they provide free remote replication for the first 12 months. This may not be a bad marketing concept.

By: snig

snig — Wed, 17 Jan 2007 16:01:00 +0000

I don’t know about EMC, but I know HDS guarantees 100% no data loss for at least 1 year. Seems some companies are more confident with their hardware than others.

I’m sure it’s not widely known that HDS does this but it wouldn’t hurt for every user to put this in their Master Purchase Agreements with all their disk vendors.

By: richard

richard — Wed, 17 Jan 2007 05:01:28 +0000

Mackem,

Well… what contractural reponsibilty does EMC assume when their customer loses data…. probably none.

By: snig

snig — Mon, 15 Jan 2007 14:28:51 +0000

I guess Chuck isn’t going to post my last response. I posted it last Thursday and it hasn’t been accepted yet. I’ll have to remember what I said and post it here later.

By: Nigel

Nigel — Fri, 12 Jan 2007 13:34:43 +0000

Personally I see the benefits being for larger drives where rebuild times are huge, and lets face it, disks are getting bigger by the day as are rebuild times.

Another issue that I would have though is that I have had several occasions where “there ahve been no spare disks in the country” and we have had to wait until the next day. This obviously is not acceptable.

By: JM

JM — Fri, 12 Jan 2007 13:25:17 +0000

That makes sense, but say your engineer takes 3 hours to get on site to replace the disk and your rebuild takes 2 hours. If the Symm fails a disk and you don’t have spares configured, your time unprotected is 5 hours. If you have spares, the rebuild kicks in automatically and your time unprotected is 2 hours. The amount of time unprotected is less with spares than without. Am I missing something?

By: SanGod

SanGod — Thu, 11 Jan 2007 23:34:30 +0000

If it’s a disk FAILURE, you’re just as unprotected during the rebuild as you are waiting – more so if the engineer can’t replace the failed disk until after the rebuild completes, which is the case with EMC.

If it’s a predictive failure, meaning that the hardware has experienced multiple single-bit failures during the scrubbing process, the spare invocation does protect you during the rebuild, as the failing disk can then be replaced without compromising redundancy.

There are a million thoughts on this, I inhereted the practice from an EMC Customer Engineer when I worked in California. A few friends of mine who are still architects have maintained. I am however considering dropping them an email to see if it’s still practiced.

By: JM

JM — Thu, 11 Jan 2007 20:10:09 +0000

I don’t have much to say about RAID6, but as far as your author’s note at the end on running spares with Symmetrix… I’ve also heard of people running no spares until the engineer shows up. Unless you’ve got performance concerns and want to schedule your rebuild to happen off-hours, I don’t think I agree with the practice. I understand what the argument is, but for me it’s all about how much time I’m vulnerable to that second disk failure. I’ll grant you that second disk is more likely to fail during the rebuild rather than under normal conditions, but every minute past when that first disk drops out of the RAID set means another minute my data is unprotected. If a spare is configured and is invoked, that amount of time is minimized as best it can be. Personally, I don’t care if the engineer has to wait before he can tell the box to spare back to the new disk or not. He can sit there and twiddle his thumbs and wait or he can remotely dial in later and do it. We’ve paid for the support contract, his inconvenience is included.