[Tig] 1Tb & 2Tb Raid disks, what make/model?

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Tue Mar 8 15:19:33 GMT 2011


On Mon, 7 Mar 2011, Bob Kertesz wrote:
>
>> Avoid the recent crop of disk drives which use 4K byte sectors
>> internally (rather than traditional 512 bytes) but pretend to use 512
>> byte sectors.  Performance with such drives generally sucks.
>
> I don't know if any drive made in the last six months or so comes in any other
> format but 4K byte sectors.

Yes, there are still such drives made.

> Those drives do quite well with Windows 7, which has been optimized to use 4K
> sectors, and from what I've read, all current SSD's use aligned 4K sectors for
> higher throughput as well. In fact, if you use most diskcopy programs to image
> an SSD from an existing hard drive, the majority of cloning software does not
> currently align to 4K sectors, and an SSD made that way will suffer in
> performance. As a result, the recommendation is almost always to do a fresh
> Win 7 install when moving to an SSD.

If your entire world revolves around Windows 7 then it is certainly 
good that it includes enhancements to work better with drives which 
secretly use 4K sectors.

For over three years I have participated in several mailing lists 
devoted to operating system filesystem implementation and design.  It 
is clear (from the wailing and performance problem reports) that the 
4K sector drives often cause severe performance impact when used in 
servers.  There are many reasons for this.  One is that 512 byte 
sectors have been the norm since at least the early '80s and so 
operating systems and filesystems have been designed and tuned for 
this sector size.  Updated operating systems and filesystems will 
surely work better with 4K sectors (especially once the disks actually 
consume 4K sectors) but it takes years to get the wrinkles worked out.

The issue is of course that any write I/O which is not aligned with a 
4K offset and 4K in size requires a performance-killing 
read/modify/write operation of one (or two) 4K sectors.  This is an 
issue because the drives support I/Os on a 512 byte boundary and 512 
bytes in size.

>> Any product with "green" in its name is surely a bad idea.
>
> Unless it's a disk drive you are just using for redundant offline storage, in
> which case they are OK and in general use less power and generate less heat
> and noise in exchange for less performance.

Green drives normally automatically park their heads or even 
automatically spin down.  Many of these drives have head park/unpark 
specifications barely over 100K cycles.  Some users of systems which 
are always active have found that their systems toast these green 
drives due to periodic writes with an interval longer than the 
automatical park interval.

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/



More information about the Tig mailing list