Feeds

Why storage needs Quality of Service

Makes shared storage play nicely

Beginner's guide to SSL certificates

Storage consolidation looks great on paper. Direct-attached storage is notorious for its inefficiency, with some arrays being just 40 per cent occupied or even less.

Providing an Oracle database with 10,000 IOPS could mean aggregating dozens of 15,000 RPM drives, and unless the database is several terabytes in size that is a lot of wasted space.

The alternative is shared storage, probably with virtualisation and thin provisioning to allocate physical disk capacity more efficiently, and perhaps with a Flash tier or cache to boost performance.

As well as reducing wastage, shared storage can also bring other advantages, not least a reduction in the number of points of management.

But what happens if one of your clients or applications doesn't play well with its fellows – if it is badly behaved and greedy and doesn't realise that in shared storage “shared” is the operative word?

In many systems, it is all too easy for one application to become the bully in the playground, grabbing too much for itself and leaving the other children crying in the dust.

Key element

“Quality of service is more crucial than people give it credit for. It's a small thing but without it a lot of the value propositions of shared storage go away,” says John Rollason, NetApp's director of product, solutions and alliances marketing.

“Essentially, if you don't have QoS on a shared storage platform, you can't guarantee overall QoS when users move to a virtualised environment. Virtualisation also makes the I/O a lot more random.”

A common example is when applications were not designed to share and have different access patterns, says Alex D’Anna, director of solutions consulting EMEA at Virtual Instruments.

“A really interesting use-case is service-hungry applications,” he says. He cites the example of a customer which had problems with its crucial SAP installation, despite apparently having plenty of SAN capacity to hand.

“SAP is there to help you manufacture, but you also need data warehousing and business analytics for forecasting. The amazing thing to us was that the customer had completely different read/write patterns and the data warehousing was completely eating up its 8Gbps Fibre Channel SAN,” D’Anna says.

He adds that the challenge is magnified once you move into the cloud. "With cloud storage, people are looking for ease of provisioning and so on. We work on the assumption that a share-everything philosophy will eventually dominate. On that platform you need a picture of what is happening," he says.

"For example, when there are performance problems people ask to be put back onto dedicated storage. But in the cloud you can't do that any more."

Feed the hungry

Frank Reichart, senior director of product marketing at Fujitsu, agrees. “QoS is necessary for storage consolidation. There is no way around that,” he says.

“If you do nothing, the server that demands the most performance will get it – and if that's your business intelligence system, then response times for the more time-critical production system will suffer. QoS also impedes the service level agreement-driven organisation, and if you cannot set QoS, you punish the user who has simple applications.”

The business intelligence (BI) problem is a big one because more and more BI users want to run their queries against the production data, not least because of the cost of setting up a dedicated data warehouse and the time needed to copy data there.

Anyone else trying to use that storage might as well take a coffee break because they are not going to get a lot done

It is not the only example, though. A heavy database query could also easily soak up all the I/O available, starving the web and email servers that are sharing the same storage. As for the impact of a VDI bootstorm on shared storage, anyone else trying to use that storage might as well take a coffee break because they are not going to get a lot done.

All of this is especially true for public-cloud operators, whose very existence and profitability is predicated on being able to share resources such as storage across multiple customers or tenants.

Increasingly this also applies to IT departments, as they too must service multiple internal clients – and typically for less and less money.

So what are the storage developers doing to deal with the issue and ensure equitable and appropriate access, without forcing you to solve the problem by expensively throwing storage at it?

The first thing is obviously to add QoS mechanisms, assigning priorities to applications. Stopping rogue applications or clients requires other approaches. One of the simpler ways to do it is to apply I/O rate limits to badly behaved applications so they don't grab everything available.

That can be too simple, advises Jesper Matthiesen, the CTO at Debriefing Software. “I don't consider bandwidth throttling to be a good thing because if the capacity is there you should use it,” he says.

Another route, and the one chosen by a number of leading-edge developers such as Fujitsu, NetApp and NexGen (now part of FusionIO), is to enforce minimum application data throughput levels rather than maximum.

Secure remote control for conventional and virtual desktops

Next page: Extra portions

More from The Register

next story
NSA SOURCE CODE LEAK: Information slurp tools to appear online
Now you can run your own intelligence agency
Azure TITSUP caused by INFINITE LOOP
Fat fingered geo-block kept Aussies in the dark
NASA launches new climate model at SC14
75 days of supercomputing later ...
Yahoo! blames! MONSTER! email! OUTAGE! on! CUT! CABLE! bungle!
Weekend woe for BT as telco struggles to restore service
Cloud unicorns are extinct so DiData cloud mess was YOUR fault
Applications need to be built to handle TITSUP incidents
BOFH: WHERE did this 'fax-enabled' printer UPGRADE come from?
Don't worry about that cable, it's part of the config
Stop the IoT revolution! We need to figure out packet sizes first
Researchers test 802.15.4 and find we know nuh-think! about large scale sensor network ops
SanDisk vows: We'll have a 16TB SSD WHOPPER by 2016
Flash WORM has a serious use for archived photos and videos
Astro-boffins start opening universe simulation data
Got a supercomputer? Want to simulate a universe? Here you go
prev story

Whitepapers

10 ways wire data helps conquer IT complexity
IT teams can automatically detect problems across the IT environment, spot data theft, select unique pieces of transaction payloads to send to a data source, and more.
The total economic impact of Druva inSync
Examining the ROI enterprises may realize by implementing inSync, as they look to improve backup and recovery of endpoint data in a cost-effective manner.
Getting started with customer-focused identity management
Learn why identity is a fundamental requirement to digital growth, and how without it there is no way to identify and engage customers in a meaningful way.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Security and trust: The backbone of doing business over the internet
Explores the current state of website security and the contributions Symantec is making to help organizations protect critical data and build trust with customers.