As the self-proclaimed storage vigilante, I will keep bringing these idiocies up as I come across them.
So, the latest “thing” now is selling systems using “Raw IOPS” numbers.
Simply put, some vendors are selling based on the aggregate IOPS the system will do based on per-disk statistics and nothing else.
They are not providing realistic performance estimates for the proposed workload, with the appropriate RAID type and I/O sizes and hot vs cold data and what the storage controller overhead will be to do everything. That’s probably too much work.
For example, if one assumes 200x IOPS per disk, and 200 such disks are in the system, this vendor is showing 40,000 “Raw IOPS”.
This is about as useful as shoes on a snake. Probably less.
The reality is that this is the ultimate “it depends” scenario, since the achievable IOPS depend on far more than how many random 4K IOPS a single disk can sustain (just doing RAID6 could result in having to divide the raw IOPS by 6 where random writes are concerned – and that’s just one thing that affects performance, there are tons more!)
Please refer to prior articles on the subject such as the IOPS/latency primer here and undersizing here. And some RAID goodness here.
If you’re a customer reading this, you have the ultimate power to keep vendors honest. Use it!
D
Technorati Tags: performance, iops
Hi D,
I am a regular visitor to your blog and have tried to understand your great tech posts …. Especially the IOPS PRIMER. now I work with netapp storage and people tell me that netapp consumes / wastes too much storage …
My reply to that is that I ask them questions : like what do you want to use it for ?I tell them the double disk failure protection without performance penalty… I tell them about storage efficiency features with which they will forget how much storage was sacrificed…
It will be great if you could do a blog post about two topics …..
How to size for e.g. if I want to have 8tb of usable space on a netapp box with dual controllers ? And another example of 20tb of SAS usable …. This will be great.
How would you explain in your words the cost effectiveness of a netapp box investment ?
Am learning always and have read quiet a few posts of yours … I want to do netapp sizing and storage calculation like a pro. I love netapp and ontap so I can take a lot of hatred and then turn it in favor of netapp. will be greatful for your expert insight and post on my requested topic
Thanks for the kind words. It’s kinda off-topic but I’d already posted something about usable space before:
http://recoverymonkey.org/2010/05/07/netapp-usable-space-beyond-the-fud/
If I were you I’d work with your local NetApp engineers, they will teach you how to do all this.
But the short answer is – sizing for usable space is not the way to do it in general, and especially with the more intelligent storage out there.
I’d size for performance first, and then factor in space savings via clones, dedupe and compression, but add on top estimated capacity needed to satisfy things like snapshots, and arrive to a final figure.
So, depending on the problem being solved, 8TB usable could become 100TB logical…
D