On Fri, Feb 27, 2015 at 2:59 PM, Chris Murphy lists@colorremedies.com wrote:
On Fri, Feb 27, 2015 at 1:53 PM, Robert Arkiletian robark@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/FD3F376DC2ECCE68882579D40082C3...
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/29C9312E3B7D10CE88257D41000D8D...
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/5...