Microsoft's Office 365, Hotmail and SkyDrive customers were left without email and other Windows Live services during an outage that lasted over three hours.
The downtime, which happened on Friday at about 4am in the UK — 8pm on Thursday Pacific time (PDT) — was due to a domain name service problem, according to Microsoft. A domain name service converts a domain name, such as ZDNet.co.uk, into an internet address such as 184.108.40.206, which is what browsers, email clients and so on use to access a service.
"Microsoft became aware of a domain name service issue causing service degradation for multiple services," the company said in a statement. "We began seeing service restoration at approximately 10.30pm PDT and achieved full service restoration at approximately 11.30pm PDT. We are conducting a review of the incident."
The outage affected customers using Office 365, Microsoft's cloud-based productivity suite, which is aimed at small to medium-sized businesses. It also affected access to Hotmail and to the SkyDrive online storage service.
People in the UK, Australia, the US, Japan and other places around the world complained in comments to the Windows Live blog that they could not use the software.
The domain name service problem was fixed by 11.49pm Pacific time, Windows Live chief Chris Jones said in a blog post on the Inside Windows Live site. It did this by making changes to its DNS configuration, which indicated the issue lay with lookups for Microsoft.com.
Microsoft doesn't claim 99.999-percent reliability. If you want a cost-effective solution, you can't expect five-nines reliability.– Andy Buss, analyst
"We have completed propagating our DNS configuration changes around the world, and have restored service for most customers," Jones said in the blog post. "Depending on your location, you may still experience issues over the next 30 minutes as the changes make their way through the network."
In general, Office 365 customers should not expect high-level, almost perfect uptime for the services, according to Freeform Dynamics analyst Andy Buss. "Microsoft doesn't claim 99.999-percent reliability," he told ZDNet UK. "If you want a cost-effective solution, you can't expect five-nines reliability."
Buss does not believe the outage reflects badly on cloud services, compared with in-house systems. "If you're running your own IT, how often has your Exchange server been taken down for servicing?" he asked.
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