The search was part of the criminal investigation into the deletion of emails on two unpopular gas plants in Oakville and Mississauga that were cancelled by the governing Liberals ahead of the 2011 election.
Investigators are examining the hard drives, which can be a "lengthy and complex process," OPP Commissioner Chris Lewis told a legislative committee.
The OPP's electronic data retrieval specialist team, who are often needed in sexual exploitation cases, are "stretched for resources" and each new case increases their workload and backlog, he said.
"So I cannot predict when this intense investigation into the allegedly deleted emails will be finished or whether charges will be laid," he added.
Lewis also didn't say what information led police to search the storage facility, saying it was contained in search warrants that have been sealed under court order.
There's another facility in Guelph with servers that store government data, he said. Computers were being stored at the Mississauga facility.
"I cannot say that charges will be laid," Lewis repeated. "I cannot say a criminal offence has occurred."
A "handful" of investigators involved in the probe of the deleted emails have interviewed more than 20 people so far, he said. Police also visited Premier Kathleen Wynne's office last November, possibly for a few hours.
"It was more looking at the layout in relation to different interviews they conducted and trying to understand the workings of the office physically — what was where, who sat where and that sort of thing," he told the committee.
There was no search warrant and the officers had the full co-operation of her staff, he said. He doesn't know if they took photos.
"It wasn't a search," Lewis told reporters after his appearance at committee.
"So they weren't crawling around looking under desks and going through closets. They wanted to see the layout of the office area. That was it."
He said he's not aware of any other instance where police had visited a premier's office in the course of a criminal investigation.
Lewis, who will step down from his post in late March, told the committee that he has no worries about the OPP's independence in the matter.
"We've arrested and charged members of Parliament in the past, from all three parties, at some point or another, I'm sure," he said. "That's just the way life goes."
He deliberately doesn't know the details of the ongoing investigation because he doesn't want to jeopardize it in any way, Lewis said.
"I could say we'd be done tomorrow and tonight we'll find out we have 50 more people to interview and I become a liar, so I really don't have a clue, and I deliberately don't have a clue," he said after repeatedly being pressed for an answer on how far along the police were in their investigation.
If a criminal offence has occurred, there are charges that could possibly be laid that could lead to jail time, he said.
Police launched a criminal probe last June after the Progressive Conservatives complained that gas plant emails were intentionally deleted by senior staff in former premier Dalton McGuinty's office.
Ontario Privacy Commissioner Ann Cavoukian found that top Liberals in McGuinty's office broke the law when they deleted emails on the cancelled gas plants prior to the 2011 election.
The opposition parties said the emails were wiped out to cover up the true costs of killing the gas plants, which the auditor general has estimated are as high as $1.1 billion.
McGuinty insisted that he never condoned or directed the deletion of emails or documents which should have been preserved under law.
It was the government's initial refusal to release gas plant documents that led to a rare and often nasty contempt of Parliament debate, which prompted McGuinty to prorogue the legislature in the fall of 2012 and resign as premier.
The Liberals eventually turned over hundreds of thousands of documents and emails related to the gas plants in several batches, insisting after each one that all the relevant correspondence had been released.
On the deleted emails, Progressive Conservative Lisa MacLeod insists there's reasonable evidence to suggest that there could have been a crime committed, which could result in jail time.
"So this is quite a serious matter," she said.
"I think that validates many of our concerns."