With Compellent, auto-tiering happens on chunks that are part of a snapshot.

So, let’s say you have a 1TB DB LUN that hosts the most absolutely critical DB in your company.

You take a snapshot of the LUN. It’s important – without the snapshot there is NO auto-tiering with Compellent (most people seem to be unaware of this).

The Compellent system is set up to move “cold” 2MB chunks of that LUN to different disks.

So, you may want the DB in RAID10, but your SATA might be configured as RAID5.

The 2MB chunks that are not being accessed frequently will end up on the RAID5 SATA space.

If you have data loss in the RAID5 space, YOU WILL LOSE YOUR LUN.

There is no magic.

Chunklet vendors like Compellent and 3Par will tell you their scheme is more reliable than straight RAID5 but here’s the simple truth:

You get a 2MB chunk.

You spread the chunk onto 5 disks if you’re doing RAID5 4+1.

If you lose any of those 2 disks you’ve lost that chunk.

End of story.

Friends don’t let friends use RAID5 in this day and age.

D

Necro from my part too i guess .

ive read it all. And its one of the best discussed storage discussions on the big http://WWW... KUDOS to all that have taken free time to discuss this.

We are evaluating Compellent (Dell now). And it looks promising (more expensive than the IBM, EMC quotes dont have any from NetApp or HP) not just for because of the tiering / dataprogression technology but quite some others like the fact that you own the software forever etc. We have an EMC CX4 now and Dell are quite keen on making us change.

One thing that is buggling my head is how the whole array handles an potential dual drive (or more) failure. And how it rebuilds…

Yes i know… hotspares, Raid6DP etc.. But it can happen. Its happened to all vendors. Bad drives, bad on-site technitian… internal human error…
Just like the EMC competitors are talking FUD about “what would happen if you would have a dual drive failure on the VAULT drives”…

What happens with Compellent if you loose several drives? Or an entire disk shelf? (lets say you plug out the wrong back end SAS cables)

In a traditional array (or server) if you loose one RAID set or have to rebuild it you dont necessarily loose (or even loose access) to your other data.

Say i devote a 15k diskshelf to my DB(and devide it into different raid sets for log, temp, DB etc)
And another diskshelf with 7,2 to file (tier3), images etc
And a third shelf to lets say VMware for different servers…

Loosing more than one drive (lets say there is no Raid6) on any of the enclosures would result in either DB or Vmware or File etc not being accessable. Which would / could be a disaster, but obviously a smaller one than if ALL the data was lost.

If a LUN is BOTH in RAID10, RAID5 and RAID6… big parts of the data are still… YES? in RAID5? Well that means that two drives going bad (statistically can happen on a bigger system with lets say 100 drives) and the hotspare cannot rebuild (i mean why do Dell quote 1 hotspare per shelf?)… well do i loose my entire SAN?
Now with all this Compellent “magic”… with “all drives participating in all raid levels/stripes” and a block / page being moved around… In a case of the above failure… having practically all drive drives in one storage pool… wouldnt the whole system go totally down? In case i loose more drives than the Raid profile protection that Compellent has can afford… and my LUNs are no longer dedicated to certain shelfs / RAID groups… would i have to restore from backup?
When a hotspare takes over / or a drive is replaced and rebuildt… surely that takes time… could be 5 hours… could be 3 days. And in the mean time all data has been moved around… what happens?

Im sure there is a smart answer… i just cant figure it out and the answers Dell are giving me are vague… kind of freaking me out!

And please dont say “remote replication” (yes that is also an option but we consider that as an option in case of a different disaster… not dual disk error.)

V.

I would like to know, how many maximum no.of clients can be configured in one NBU 6.5 master server (so far we have configured around 1000 clients) and best practices realted to it?

And i want to know what is netbackup 6.5 catalog databse maximum capacity?

I wonder what would be the performance like in a scenario where we have a multithreaded workload? I think XFS would perform really well, not sure about others though,

As a guy involved in the NetApp vs EMC vs Compellent decision cycle right now, I found this post amazingly helpful.

NOT because I will take what was posted verbatim, but rather as I believe it is intended, and that is to ask probing questions of *all* vendors about the issues raised here.

Perhaps I am atypical, but as a Director guy who is one step removed from day to day management of these systems, it is this and similar posts that really help me understand what is relevant to my business model. It is this information that helps me work with the team to ask the questions that will get the techs out of the data center in and into the business, where we can make a REAL difference.

Would you mind letting me know what company you work at? You could drop me a private line if you don’t want to share publicly.

I would very much like to know how you calculated the price. But I think I already know.

You see, there have been major changes since the July pricing you are looking at, rendering all the cache boards completely free of charge for the SPEC configuration (each 6240 or 6280 node now gets a no-cost 512GB cache added plus one protocol, in this case NFS).

There have also been other reductions, everything I mentioned combined making the price difference compared to the July pricing over $2.8m. Do the subtraction and compare to the original figure I posted

So our pricing was absolutely list, and nobody’s trying to slip anything past anyone. I didn’t post a link to our pricing since I’m not aware of a current price sheet that’s internet-accessible through our site. But anyone can contact their VAR and have this priced.

A blog such as this is a very public document indeed – my personal and professional reputation are on the line every time I post, so I go beyond the “measure twice, cut once” rule and frequently measure 4-5 times… (which also explains why I don’t post daily like some folks do – solid research takes time plus blogging is not my day job).

Let me know if you’d like more clarification.

Finally, nobody is unbiased. Read this: http://wp.me/p1k3XN-28

D

I read this paper when it was first released and i thought it seemed off but dismissed it since i didn’t have the time. I believe everyone above has brought up most of the technical questions i would ask so for now i’ll leave that out. I would like to mention that we currently have both NetApp and EMC in our environment so i’m as unbiased as can be.

But the question i am going to ask is why are you incorrectly stating the cost of the NetApp configuration. I know the Isilon system is priced correctly since you were kind enough to post the link to the EMC master pricing list, but i found it weird you didn’t post one to yours… So i decided to go and find some prices on the offical NetApp site which i eventually did.

So when using your items list on the SpecFS paper, the price comes to almost 9,000,000 and thats WITHOUT the 8.1 cluster mode license since its not listed on the July 11 contract i was looking at.

I’m curious how your comments about being 50% cheaper then are true. Or were you trying to slip that past us, that EMC was list pricing while yours isn’t.

This is troubling to a purchaser like myself when a company needs to falsify there information to make there company look better.

I’m not sure how you conclude this is misleading anyone.

So please do not mislead the audience by saying NetApp can achieve a higher NFS IOPs count with a lower configuration