2011/3/29 Jeff <threshar@xxxxxxxxxxxxx>: > > On Mar 29, 2011, at 12:13 AM, Merlin Moncure wrote: > >> >> My own experience with MLC drives is that write cycle expectations are >> more or less as advertised. They do go down (hard), and have to be >> monitored. If you are writing a lot of data this can get pretty >> expensive although the cost dynamics are getting better and better for >> flash. I have no idea what would be precisely prudent, but maybe some >> good monitoring tools and phased obsolescence at around 80% duty cycle >> might not be a bad starting point. With hard drives, you can kinda >> wait for em to pop and swap em in -- this is NOT a good idea for flash >> raid volumes. > > > > we've been running some of our DB's on SSD's (x25m's, we also have a pair of > x25e's in another box we use for some super hot tables). They have been in > production for well over a year (in some cases, nearly a couple years) under > heavy load. > > We're currently being bit in the ass by performance degradation and we're > working out plans to remedy the situation. One box has 8 x25m's in a R10 > behind a P400 controller. First, the p400 is not that powerful and we've > run experiments with newer (p812) controllers that have been generally > positive. The main symptom we've been seeing is write stalls. Writing > will go, then come to a complete halt for 0.5-2 seconds, then resume. The > fix we're going to do is replace each drive in order with the rebuild > occuring between each. Then we do a security erase to reset the drive back > to completely empty (including the "spare" blocks kept around for writes). > > Now that all sounds awful and horrible until you get to overall performance, > especially with reads - you are looking at 20k random reads per second with > a few disks. Adding in writes does kick it down a noch, but you're still > looking at 10k+ iops. That is the current trade off. > > In general, i wouldn't recommend the cciss stuff with SSD's at this time > because it makes some things such as security erase, smart and other things > near impossible. (performance seems ok though) We've got some tests planned > seeing what we can do with an Areca controller and some ssds to see how it > goes. > > Also note that there is a funky interaction with an MSA70 and SSDs. they do > not work together. (I'm not sure if HP's official branded ssd's have the > same issue). > > The write degradation could probably be monitored looking at svctime from > sar. We may be implementing that in the near future to detect when this > creeps up again. svctime is untrustable. From the systat author, this field will be removed in a future version. -- Cédric Villemain 2ndQuadrant http://2ndQuadrant.fr/ ; PostgreSQL : Expertise, Formation et Support -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
