This is worth a repost (from : @He9ePpy-hgi ), I am not the author but it's the best summary of what's going on at WD that I've seen so far...
WD Irvine primarily focuses on hard drives for desktop and laptop computers. Fewer laptops and destops use hard drives - they use a faster kind of storage - solid state drives - to store data. Also, more users store their data (photos, videos, documents, etc.) on the Cloud. Essentially, storage on "the Cloud" means storing data on hard drives that are located far away in a data center, usually, and retrieiving it online.
WD had projected a drop in demand for destop and laptop hard drives. But the projection proved too optimistic. In early 2015, there was a sudden drop in sales. Departments were ordered to cut costs. That resulted in layoffs at WD Irvine, including a number of fairly senior people up to the Director level.
WD Irvine hoped the drop in sales was related to the economy, and that hard drive sales would pick up, but demand just kept plunging. The market reacted. The stock price fell from over $100/share in early 2015, to about $39/share today.
Meanwhile, WD had purchased another company - Hitachi Global Storage (HGST) - which focuses more on the type of hard drives that are used in the Cloud and also that large companies use in data center. The word "Enterprise" refers generally to this type of hard drive. Since enterprise drives are often heavily used, in an environment much more demanding than on the typical home PC or laptop, the enterprise drives must be especially reliable and durable. HGST is very good at this type of harddrive, while WD Irvine has been weaker.
Enterprise drives are now thought to be the primary drives for the future, as data from mobile phones, tablets, and now laptops and PC's is frequently stored on the type of enterprise drives that HGST makes. So WD is now primarily looking to HGST (headquartered in San Jose) to develop and make the hard drives of the future. WD Irvine, it appears, is becoming less relevant to the company, which partially explains the layoffs in Irvine - which many are speculating will be significant and will occur over the next several months. HGST recently completed construction on a new headquarters building in San Jose that WD owns (WD's space in Irvine is leased), and the San Jose-based leader of HGST recently became President of the whole company. There is considerable speculation that WD headquarters will leave Irvine and move to San Jose.
One other factor: WD and HGST both make hard drives at facilities overseas. Now that the companies are merging (which the Chinese government held up for a couple years over, officially at least, anti-trust concerns), manufacturing facilities can be combined. The company doesn't need so many facilities that make the same thing. So thousands of factory workers are expected to be laid off as their manufacturing facilities are closed. WD has already shut down one facility, in Japan. Other operations are expected to be eliminated at faciliities in Malaysia and perhaps other countries.
WD management has promised Wall Street that it will save several hundred millions of dollars by reducing operating expenses at the combined companies, presumably by shutting down manufacturing facilities (overseas primarily) and by reducing redundancies in operations in the US (e.g. no need for separate R&D groups, hardware development, administrative, legal, etc.) and laying off a lot of WD employees - most likely in the thousands, but only top management has an idea of how many employees will be cut.
WD is in the midst of purchasing another company - SanDisk - which does not make hard drives but instead makes solid state memory. This is the type of memory that mobile phones & tablets use, and that laptops & desktops are quickly adopting. HGST also devlops solid state memory, but SanDisk is better at it. There is speculation that HGST will cut its own efforts to develop solid state technology, and that there will be layoffs at HGST in that group.
WD Irvine laid off a lot of good, experienced, talented people in 2015. The scale of layoffs in 2016 is widely believed to be much more significant. Rumors on the Internet are that a wave of large-scale cuts are imminant. Some are reporting that the "slider" manufacturing operation in Penang, Malaysia has been cut within the past few days (sliders are a component of a hard drive) and that the slider manufacturing equipment is now being shipped to WD's plant in Thailand. That means layoffs of many factory workers and even higher-level people in Penang. As mentioned above, this trend of consolidating operations is expected to continue for some time.
That's some background - some of it is solid and well-documented, while some of it is based on widely-believed speculation. Many workers - especially those at WD Irvine - are quite concerned for their future. Workers who have deep experience in hard drives are concerned that since hard drive sales are dropping so fast, they won't be able to find another hard drive-related job, or maybe any job at all. Time will tell.