Drobo

Write caching

Do drobos support write caching? The big problem with redundant disk arrays is that both reads and writes inevitably have to read/write at least two disks. The reads can sometimes optimise the process (e.g. mirrored drives can use “first past the post” to minimise rotational delays) but the writes were always a problem.

To overcome this, RAID cards sometimes have a write cache with a battery backup. My office one does. So writes go at cache speed. In the event of a power failure, I have 24 hours to get the power back before I face data loss. Given the cheapness of memory, and its low power consumption, it should be simple to include a battery backed write cache in drobos.

As it happens, I run my drobo on a UPS, so I don’t even need the battery. If there were an option, I could enable write caching in safety. I already have write caching enabled in Windows, but more is always better!

The DroboPro definitely does. PC Perspective did a full review including ripping apart the hardware to see what was inside.
http://www.pcper.com/article.php?aid=792

http://support.datarobotics.com/app/answers/detail/a_id/162

“Power failure: Every Drobo storage device has a battery-backed cache memory. This protects its meta data, which is information the device uses to keep track of where data is written on the drives and which parts of the drives are in use. A sudden power failure usually induces total data loss on external drives if they are writing data when the power fails. This is because the meta data for the file system is stored on the computer, not on the external drive. Power failure during a write means this meta data doesn’t make it to the disk. Your Drobo device protects it by first writing to its battery-backed cache and then to the disk. If a power failure occurs, the device knows the state of the disk and protects it. Data loss is limited only to that being written by the computer’s OS to the Drobo device, not the hundreds of GB of data already on your Drobo product.”