Help StorageMojo find the VMAX 20k’s lost petabytes!

by Robin Harris on Wednesday, 21 January, 2015

While working on a client configuration for a VMAX 20k – and this may apply to the 40k as well, as I haven’t checked – I encountered something odd: The 20k supports up to 2400 3TB drives, according to the EMC 20k spec sheet. That should be a raw capacity of 7.2PB

However, the same spec sheet appears to say that the maximum usable storage capacity – after taking care of formatting overhead, system needs, etc. is ≈2PB. Here’s the table from the spec sheet:

20k spec sheet

Coming at it from other directions, it seems that since the 20k supports four 60 drive enclosures per rack, and supports 10 drive racks – with a lot of daisy-chaining – you can indeed connect 2400 3.5″ SAS drives. So where us the discrepancy?

Try as I might I can’t reconcile it. Simple spec sheet error? I can’t read? Are large capacity drives short stroked? Is the NSA using the rest? What’s up?

I know there’s a lot of EMC expertise out there, so please, enlighten me!

The StorageMojo take
I’ve been looking at a number of systems this week. As far as large vendor product info goes, EMC and NetApp are the least forthcoming, HP the most, and HDS in the middle.

Normally withholding information from customers is meant to ensure a call to their friendly Sales Engineer, but perhaps it is to imbue passivity into customers. “Boy, I can’t figure this out. Why even try?”

Perhaps more on this topic later. I’ve also thought of twist on the Price Lists that may justify un-deprecating them. Your thoughts?

Courteous comments welcome, of course. Update: If I were in competitor product marketing, especially for flash products, I’d be updating my “flash is competitive with disk” slides tonight. End update.

{ 4 comments… read them below or add one }

Chris M Evans January 21, 2015 at 1:18 pm


I doubt you will ever be able to work it out from the spec sheet. When you look at the capacities for mirrored versus RAID-5(3+1) the expected values are different for the minimum figures and for 146GB drives. However the maxima for 146GB and 3TB drives are the same, implying that you cannot configure an array with 2400 3TB drives – there is a lower artificial limit on drive count.

However even that number is hard to work out. The 146GB drives claim a usable 143.5GB usable for Open Systems formatting. But multiply up 48 of them and divide by two and you’re well short of the quoted TB capacity of 2.8TB

What’s not clear is whether 1TB = 1000GB (although 1GB is quoted as 1000^3). Also there’s no clarity on the overhead per each drive.

You’re on a losing streak trying to work it out – I’ve done this for a long time using real data from the array and it still comes up like a magical calculation.

Sean Luce January 21, 2015 at 3:00 pm

Are you factoring in disks lost to parity or RAID1 mirroring? That accounts for a good amount. Is there a max marketed capacity of 2PB? Regardless of the RAID type chosen, the max capacity stays about the same. They should be quite different depending on the RAID type chosen.

Peter Serocka January 25, 2015 at 9:21 pm

VMAX 20K: 3200 drives max, 2PB max

whatever limit is reached first… so 2000 or 3000 of 3TB drives would simply not considered a reasonable/valid configuration.

— Peter

MCH February 4, 2015 at 7:09 am

Hello Robin! Long time reader of yours.

You actually touched on the very troubling trends demonstrated in the ‘demand’ half of the Economics 101 concept of ‘supply and ‘demand’. Customers aren’t demanding enough in the area of Storage Software Quality.

I manage the storage administration, monitoring, and reporting software tools at my organization. Here’s my take…

EMC has excellent hardware and support facilities (Isilon, not so much, yet). However, the devil is always in the details… that ‘make vs. buy’ thing isn’t working out very well for their software products division (name any of them). They are maturing, and have had interesting management changes of late. Too many buzzwords in their ‘technical whitepapers’ give me the heebie jeebies.

NetApp’s software (my experience was limited to a 4 month evaluation of the old SANScreen product) was, on the other hand, very forward looking and actually worked as advertised in most cases. This showed their understanding of what ‘Enterprise Grade Software’ actually meant. To me that means: ‘Give some guy in an understaffed and overwhelmed storage department SOMETHING that he can actually implement without so many ‘gotchas’ that he can focus on producing useful information for his business… instead of spending most of his time submitting tedious bug reports and uploading diagnostics all GD day…’ (rant over)

HDS: I know terribly little about HDS, but sucesses from my peers in this region has me curious, at least. From my ‘grunt storage admin’ point of view, my vendor criteria puts much weight on what kind of corporate culture you want to support you during panic attack support call? Reading employee comments on Glassdoor is quite insightful.

Leave a Comment

Previous post:

Next post: