Microsoft UK has vowed to provide BPOS customers with vouchers against future credits following seven hours of downtime at the weekend.

This is the latest in a series of embarrassing cloud outages for Redmond after a summer of interruptions began in May, but differs from other incidents in that an "Act of God" was responsible for knocking out the service.

This is after bolt of lightning struck a transformer close to the Dublin-based data centre powering BPOS, causing an explosion and fire that took out the utility and back-up generators, resulting in a total power wipe-out.

A Microsoft spokesman told The Reg it will "proactively provide impacted customers with a 25 per cent credit on a future monthly invoice".

The timing of the BPOS crash was relatively lucky for Microsoft as a seven-hour incident mid-week may have turned customers into gang of marauding teenagers.

But all this calls into question the value of the financially backed SLA offered by Redmond: customers with a monthly uptime lower than 95 per cent get a full discount; a 50 per cent credit on uptime between 95 per cent 99 per cent; and a 25 per cent note for uptime between 99 per cent and 99.9 per cent.

This means that customers experiencing anything above 8.76 hours of downtime a year are able to make a claim against the Ts&Cs in Microsoft's SLA.

The SLA does not apply when the service is hit by availability issues arising from "factors outside of our control" – one of the criteria.

Another interesting boast from Microsoft, and one that appears of equally dubious value, is its claim that blackouts should never be a concern for prospective cloud customers.

"When you switch to cloud power Microsoft, you never have to worry about a power outage. You can rest easy. Our financially backed 99.9 per cent uptime guarantee means a steady stream of power is pumped directly into your business at all times and include 24/7 support if anything ever does go wrong," said the vendor on its website.

Resellers should take note when advising customers to switch to Office 365, the successor to BPOS, as Microsoft previously admitted that outages on the new cloud service are also inevitable. ®