On 2013-03-06, Gordon Messmer <yinyang at eburg.com> wrote: > On 03/06/2013 12:28 PM, Keith Keller wrote: >> Please Note: 1) The default of the unit creation sets write cache >> to "on" for performance reasons. However, if there is no BBU >> available for the controller, a warning is sent to standard error. > > It is a warning that there is no BBU, not a warning that you'll get > unsafe write caching without one. > > To the best of my recollection, all controllers will turn off write > caching if the battery fails and during the battery re-learn cycle. If > there is no BBU present, caching will never be enabled. Unfortunately, I don't have an available machine on which to test. But at one point I believe that I did have a 9550-backed controller with no BBU which would allow me to turn on write caching for a redundant array. I know that this same machine does say that the write cache is "on" for the JBOD units it currently hosts. (It's a tertiary backup on a data center power grid, so the likelihood of sudden power loss is low, and if the filesystem is lost I wouldn't be all that upset.) >> But if LSI >> starts phasing out the 3ware line perhaps it makes sense for people to >> start looking at MegaRAID controllers to be prepared for this >> possibility. (The minimal web searching I've done seems to support the >> dauntiness of the MegaRAID tools.) > > Whether or not LSI continues to make 3ware cards, I continue to strongly > recommend against their use. They suck. They have always sucked. If a > customer wanted me to manage a system with a 3ware card in it, I'd > decline because at some point I'm going to be paged during off hours to > fix the damn thing. This is surprising to me. I've had one 3ware controller fail in 10 years. Two caveats to this note are that the failure ended up destroying the filesystem, and I'm not happy with another 3ware controller I have (the aforementioned 9550, which is very old). To throw Yet Another Monkey Wrench into the discussion, I know that some of the CentOS folks swear by Areca controllers. So YMMV in any case. --keith -- kkeller at wombat.san-francisco.ca.us