24 Apr
2018
24 Apr
'18
10:59 a.m.
On Mon, Apr 23, 2018 at 10:49 PM, Bakul Shah <bakul(a)bitblocks.com> wrote:
On Mon, 23 Apr 2018 22:32:26 -0600 Grant Taylor via
TUHS <
tuhs(a)minnie.tuhs.org> wrote:
That's right. This is for BIO_ZONE stuff, which has to do with host managed
and host aware SMR drive zones. That's different than the zones you are
talking about.
I had always assumed that the outer edge (what I thought was the end of
the disk) was faster than the inner edge (what I thought was the
beginning of the disk) because of geometry. However, as Ronald stated,
hard drives were constant angular density. Thus negating what I
originally thought about speed.
Constant angular velocity means faster "linear" velocity for
tracks further away from the center. Since 1990 or so disk
tracks are divided up in 16 or so "zones", where outer zones
have more blocks per track. This translates to higher
throughput.
A modern Seagate Exos SAS disk may have a range of 279MB/s
(outermost) to 136MB/s (innermost) or 300MB/s to 210MB/s for
faster disks (15Krpm). Disk vendors don't seem to break this
range out for consumer drives. But you can measure it using
tools like diskinfo on FreeBSD. For example:
# diskinfo -t /dev/ada4 # this is an 5 year old 1TB WD "Black" disk.
/dev/ada4
...
Not_Zoned # Zone Mode <<== this seems wrong.
...
Transfer rates:
outside: 102400 kbytes in 0.972176 sec = 105331
kbytes/sec
middle: 102400 kbytes in 1.088977 sec = 94033
kbytes/sec
inside: 102400 kbytes in 1.804460 sec = 56748
kbytes/sec
Yes. This matches our experience where we get 1.5x better on the low LBAs
than the high LBAs. We're looking to 'short stroke' the drive to the first
part of it to get better performance... Toss a filesystem on top of it, and
have a more random workload and it's down to about 30% better than using
the whole drive....
Warner