Activist investor Elliott Management Corp. has bought a sizable stake in Public Storage and nominated six directors to the board of the real estate investment trust, according to a person familiar with the matter.

It’s unclear what Elliott’s plans are for the Glendale, California-based operator of storage facilities, the person said, asking not to be identified as the information isn’t yet public. An Elliott official declined to comment, and Public Storage couldn’t be reached after regular business hours.

The stake purchase came as Public Storage shares gained just 3.3% this year, compared with the 13% increase in the S&P 500 Index. Still, it has outperformed the S&P index tracking 31 real estate stocks, which has fallen 6.7%.