Zeugswetter Andreas DAZ SD wrote: > > >> Are you sure about that? That would probably be the normal case, but > >> are you promised that the hardware will write all of the sectors of a > > >> block in order? > > > > I don't think you can possibly assume that. If the block > > crosses a cylinder boundary then it's certainly an unsafe > > assumption, and even within a cylinder (no seek required) I'm > > pretty sure that disk drives have understood "write the next > > sector that passes under the heads" > > for decades. > > A lot of hardware exists, that guards against partial writes > of single IO requests (a persistent write cache for a HP raid > controller for intel servers costs ~500$ extra). > > But, the OS usually has 4k (some 8k) filesystem buffer size, > and since we do not use direct io for datafiles, the OS might decide > to schedule two 4k writes differently for one 8k page. > > If you do not build pg to match your fs buffer size you cannot > guard against partial writes with hardware :-( > > We could alleviate that problem with direct io for datafiles.
Now that is an interesting analysis. I thought people who used batter-backed drive cache wouldn't have partial page write problems, but I now see it is certainly possible. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
