"Vertical integration is really key to winning in the enterprise storage market," Mehrotra said. Solid-state drives, or SSDs, are faster than traditional hard-disk drives and while they are still more expensive than traditional drives, they are increasingly being built into laptop PCs. Flash drives are also being adopted by data centers, a market where SanDisk competes with rivals such as Western Digital Corp WDC.O. SanDisk's offer of $11.25 per share represents a premium of 21 percent to Fusion-io's Friday close but is 40 percent less than Fusion-io's IPO price of $19 in 2011. Fusion-io's shares were up 23 percent at $11.45 on Monday, suggesting that some investors expect a higher offer. Nandury Summit Research Partners analyst Srini Nandury said rival bids were unlikely since other storage companies, including Western Digital and Toshiba Corp 6502.T, bought SSD makers last year.