yes, big arrays (symmetrix, shark) have battery backed everything - enough to take all the cache and dump it to disk when power is lost. terabytes of RAM. they

yes, big arrays (symmetrix, shark) have battery backed everything - enough to take all the cache and dump it to disk when power is lost. terabytes of RAM. they also often use use a flash cache behind the RAM - that was the primary use for Optane. The reason for this, is sustained writes instead of peaks. If you let more and more sit in cache, eventually you have write folding. That results in less write IO on the backend, and you're able to have a higher sustained peak. smaller cheaper arrays (unity, pure, isilon) and HCI (nutanix, vxrail) that don't have terabytes of RAM - they have gigabytes, and pretty much always use flash as a write cache. In fact, I cannot name one that doesn't. No one in enterprise storage cares about the indurance of flash. All that means is that twice a year, a vendor engineer comes out to replace a few flash drives under your support contract. And flash has been used as a write cache behind a smaller RAM cache, for two decades, by all major storage vendors.