On Thu, May 16, 2013 at 11:46 AM, Merlin Moncure <mmonc...@gmail.com> wrote:
> On Thu, May 16, 2013 at 1:34 PM, Jeff Janes <jeff.ja...@gmail.com> wrote: > > On Thu, May 16, 2013 at 7:46 AM, Cuong Hoang <climbingr...@gmail.com> > wrote: > >> > >> Hi all, > >> > >> Our application is heavy write and IO utilisation has been the problem > for > >> us for a while. We've decided to use RAID 10 of 4x500GB Samsung 840 Pro > for > >> the master server. I'm aware of write cache issue on SSDs in case of > power > >> loss. However, our hosting provider doesn't offer any other choices of > SSD > >> drives with supercapacitor. To minimise risk, we will also set up > another > >> RAID 10 SAS in streaming replication mode. For our application, a few > >> seconds of data loss is acceptable. > >> > >> My question is, would corrupted data files on the primary server affect > >> the streaming standby? In other word, is this setup acceptable in terms > of > >> minimising deficiency of SSDs? > > > > > > > > That seems rather scary to me for two reasons. > > > > If the data center has a sudden power failure, why would it not take out > > both machines either simultaneously or in short succession? Can you > verify > > that the hosting provider does not have them on the same UPS (or even > worse, > > as two virtual machines on the same physical host)? > > I took it to mean that his standby's "raid 10 SAS" meant disk drive > based standby. I had not considered that. If the master can't keep up with IO using disk drives, wouldn't a replica using them probably fall infinitely far behind trying to keep up with the workload? Maybe the best choice would just be stick with the current set-up (one server, spinning rust) and just turn off synchrounous_commit, since he is already willing to take the loss of a few seconds of transactions. Cheers, Jeff
