Cloud storage company Dropbox's initial public offering was oversubscribed, two people familiar with the matter have said.

This indicates healthy demand for the first big tech IPO this year despite tech stocks opening the week on a sour note. 

While investor appetite looked encouraging with three days to go before final pricing, it was not clear if that would be strong enough to lift the deal above of the initial range of $16 to $18 a share that Dropbox set last week. 

The offering is expected to price Thursday, and the stock will start trading on the Nasdaq on Friday. 

Dropbox's IPO comes in what is sizing up to be a challenging week for stocks, with the US Federal Reserve set to raise interest rates on Wednesday, a day before the Dropbox deal is set to close. 

Tech shares also fell hard to open the week, with Nasdaq down more than 2% on reports of Facebook's latest data privacy problems. 

Dropbox's IPO also comes on the heels of an upsized deal last week from cyber security firm Zscaler.

It is being watched as a barometer of investor enthusiasm for tech unicorns - young companies valued at more than $1 billion - after Snapchat owner Snap's shares cratered following a much-touted IPO a year ago. 

Dropbox and existing stockholders are selling 36 million shares, and the offering could be increased by 5.4 million if underwriters exercise their right to buy more stock. 

At the high end of the indicated pricing, it could raise nearly $650m, making it the largest tech IPO since Snap hit the market just over a year ago.

The current price range suggests the San Francisco company, co-founded in 2007 by Andrew Houston and Arash Ferdowsi, will hit the public market valued at roughly $7 billion, a hefty discount to the $10 billion implied by its last funding round in 2014. 

Houston is the largest shareholder and will retain 24% of Dropbox after selling 2.3 million shares in the offering. 

Sequoia Capital is the largest shareholder among outside investors, with about a 25% stake. 

The company has 500 million users and competes with Google, Microsoft, and has Box Inc as its main rival.