On Fri, Feb 27, 2015 at 2:59 PM, Chris Murphy <lists at colorremedies.com> wrote: > On Fri, Feb 27, 2015 at 1:53 PM, Robert Arkiletian <robark at gmail.com> > wrote: > > Still have good quality older sata hardware raid cards that require 512 > > bytes/sector. As far as I know HD manufacturers are not making native 512 > > bytes/sector drives any more. > > 512n drives still exist, although they tend to be a bit smaller, 2TB or > less. > > http://www.hgst.com/tech/techlib.nsf/techdocs/FD3F376DC2ECCE68882579D40082C393/$file/US7K4000_ds.pdf > > I too noticed that HGST (now owned by WD) makes native 512n drives. That pdf states that they come in 2,3,4 TB models. (A6 in the model # represents 512n). But there are almost no reviews on these HGST native 512n drives online. > 4Kn drives are appearing now also. I don't expect these drives to be > bootable except possibly by systems with UEFI firmware. It's also > possible hardware RAID will reject them unless explicitly supported. > > http://www.hgst.com/tech/techlib.nsf/techdocs/29C9312E3B7D10CE88257D41000D8D16/$file/Ultrastar-7K6000-DS.pdf > > > > Some have better 512e emulation than others. Looking for some advice on > > which to avoid and which are recommended. Thanks. PS this is for a > CentOS6 > > server. > > The emulation implementations don't come into play if the alignment is > correct from the start. The better implementations have significantly > less pathological behavior if alignment is wrong, but that's > anecdotal, I don't have any empirical data available. But I'd say in > any case you want it properly aligned. > According to this pdf [1] alignment is important but from what I understand 512e emulation still has a small RMW performance hit from writes that are smaller than 4k or if the writes are not a multiple of 4k. Also it's probably not a good idea to mix 512e with 512n in a raid set. Although this may be hard to avoid as drives fail in the future. [1] http://i.dell.com/sites/doccontent/shared-content/data-sheets/en/Documents/512e_4Kn_Disk_Formats_120413.pdf