<s>
Shingled	B-Device
magnetic	I-Device
recording	I-Device
(	O
SMR	O
)	O
is	O
a	O
magnetic	B-Architecture
storage	I-Architecture
data	O
recording	O
technology	O
used	O
in	O
hard	B-Device
disk	I-Device
drives	I-Device
(	O
HDDs	O
)	O
to	O
increase	O
storage	B-Device
density	I-Device
and	O
overall	O
per-drive	O
storage	O
capacity	O
.	O
</s>
<s>
Conventional	O
hard	B-Device
disk	I-Device
drives	I-Device
record	O
data	O
by	O
writing	O
non-overlapping	O
magnetic	O
tracks	O
parallel	O
to	O
each	O
other	O
(	O
perpendicular	B-Device
magnetic	I-Device
recording	I-Device
,	O
PMR	B-Device
)	O
,	O
while	O
shingled	B-Device
recording	I-Device
writes	O
new	O
tracks	O
that	O
overlap	O
part	O
of	O
the	O
previously	O
written	O
magnetic	O
track	O
,	O
leaving	O
the	O
previous	O
track	O
narrower	O
and	O
allowing	O
higher	O
track	O
density	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
SMR	O
drives	O
are	O
divided	O
into	O
many	O
append-only	B-General_Concept
(	O
sequential	O
)	O
zones	O
of	O
overlapping	O
tracks	O
that	O
need	O
to	O
be	O
rewritten	O
entirely	O
when	O
full	O
,	O
resembling	O
flash	O
blocks	O
in	O
solid-state	B-Device
drives	I-Device
.	O
</s>
<s>
Device-managed	O
SMR	O
devices	O
hide	O
this	O
complexity	O
by	O
managing	O
it	O
in	O
the	O
firmware	O
,	O
presenting	O
an	O
interface	O
like	O
any	O
other	O
hard	B-Device
disk	I-Device
.	O
</s>
<s>
While	O
SMR	O
drives	O
can	O
use	O
DRAM	O
,	O
flash	B-Device
memory	I-Device
,	O
and	O
even	O
a	O
portion	O
of	O
their	O
own	O
platter	B-Device
reserved	O
for	O
use	O
with	O
PMR	B-Device
instead	O
of	O
SMR	O
,	O
as	O
a	O
cache	B-General_Concept
to	O
improve	O
writing	O
performance	O
,	O
continuous	O
writing	O
of	O
large	O
amount	O
of	O
data	O
is	O
noticeably	O
slower	O
than	O
with	O
PMR	B-Device
drives	O
.	O
</s>
<s>
Seagate	O
started	O
shipping	O
device-managed	O
SMR	O
hard	B-Device
drives	I-Device
in	O
September	O
2013	O
,	O
stating	O
an	O
increase	O
in	O
overall	O
capacity	O
of	O
about	O
25%	O
compared	O
to	O
non-shingled	O
storage	O
.	O
</s>
<s>
In	O
September	O
2014	O
,	O
HGST	O
announced	O
a	O
10TB	O
drive	O
filled	O
with	O
helium	O
that	O
uses	O
host-managed	O
shingled	B-Device
magnetic	I-Device
recording	I-Device
,	O
although	O
in	O
December	O
2015	O
it	O
followed	O
this	O
with	O
a	O
10TB	O
helium-filled	O
drive	O
that	O
uses	O
conventional	O
non-shingled	O
perpendicular	B-Device
recording	I-Device
.	O
</s>
<s>
Western	O
Digital	O
,	O
Toshiba	O
,	O
and	O
Seagate	O
have	O
sold	O
SMR	O
drives	O
without	O
labeling	O
them	O
as	O
such	O
,	O
generating	O
a	O
large	O
controversy	O
,	O
as	O
SMR	O
drives	O
behave	O
much	O
more	O
slowly	O
under	O
some	O
circumstances	O
(	O
such	O
as	O
random	O
writes	O
)	O
than	O
PMR	B-Device
drives	O
.	O
</s>
<s>
These	O
mislabeling	O
practices	O
were	O
used	O
in	O
both	O
consumer-centric	O
and	O
dedicated	O
data	O
storage	O
HDDs	O
for	O
servers	O
,	O
NASes	B-Application
,	O
RAIDs	B-Architecture
,	O
and	O
cold	B-General_Concept
storage	I-General_Concept
.	O
</s>
<s>
The	O
severe	O
interference	O
from	O
the	O
adjacent	O
tracks	O
was	O
partially	O
mitigated	O
by	O
the	O
use	O
of	O
slant	O
azimuth	B-Device
recording	I-Device
.	O
</s>
<s>
The	O
disk	B-General_Concept
controller	I-General_Concept
in	O
a	O
device-managed	O
drive	O
internally	O
handles	O
any	O
re-writing	O
required	O
by	O
the	O
special	O
characteristics	O
of	O
a	O
shingled	O
drive	O
,	O
similar	O
to	O
the	O
way	O
a	O
flash	B-Device
memory	I-Device
controller	I-Device
internally	O
handles	O
re-writing	O
required	O
by	O
the	O
special	O
characteristics	O
of	O
flash	B-Device
media	I-Device
.	O
</s>
<s>
Its	O
firmware-controlled	O
shingle	O
translation	O
layer	O
operation	O
can	O
be	O
compared	O
to	O
solid-state	B-Device
drives	I-Device
,	O
as	O
LBA	B-Device
addresses	O
do	O
not	O
correlate	O
much	O
to	O
on-disk	O
structure	O
.	O
</s>
<s>
The	O
append-only	B-General_Concept
zones	O
are	O
very	O
slow	O
for	O
random	O
writing	O
,	O
so	O
writes	O
are	O
first	O
sent	O
to	O
a	O
PMR	B-Device
cache	B-General_Concept
,	O
and	O
the	O
disk	O
moves	O
these	O
data	O
to	O
SMR	O
parts	O
when	O
idle	O
.	O
</s>
<s>
RAID	B-Architecture
resilvering	O
tends	O
to	O
overload	O
the	O
cache	B-General_Concept
,	O
sending	O
SMR	O
drives	O
into	O
minutes-long	O
pauses	O
.	O
</s>
<s>
Both	O
behaviors	O
tend	O
to	O
be	O
interpreted	O
as	O
drive	O
failure	O
by	O
the	O
RAID	B-Architecture
controller	O
.	O
</s>
<s>
The	O
zoned	O
nature	O
of	O
SMR	O
also	O
means	O
that	O
the	O
disk	O
suffers	O
from	O
write	B-Error_Name
amplification	I-Error_Name
when	O
garbage	B-General_Concept
collecting	I-General_Concept
,	O
although	O
for	O
hard	B-Device
drives	I-Device
the	O
main	O
problem	O
with	O
writes	O
is	O
speed	O
instead	O
of	O
longevity	O
.	O
</s>
<s>
Some	O
SMR	O
hard	B-Device
drives	I-Device
support	O
the	O
TRIM	O
command	O
for	O
this	O
reason	O
.	O
</s>
<s>
Two	O
sets	O
of	O
specialized	O
commands	O
,	O
ZBC	O
(	O
Zoned	O
Block	O
Commands	O
,	O
ANSI	O
INCITS	O
536	O
)	O
for	O
SCSI	B-Architecture
and	O
ZAC	O
(	O
Zoned	O
ATA	O
Commands	O
,	O
ANSI	O
INCITS	O
537	O
)	O
for	O
SATA	O
are	O
available	O
for	O
SMR	O
devices	O
.	O
</s>
<s>
They	O
tell	O
the	O
host	O
about	O
whether	O
each	O
zone	O
is	O
PMR	B-Device
or	O
SMR	O
and	O
allow	O
them	O
to	O
address	O
these	O
zones	O
directly	O
.	O
</s>
<s>
Each	O
zone	O
has	O
a	O
range	O
of	O
LBA	B-Device
addresses	O
associated	O
with	O
it	O
,	O
and	O
all	O
LBA-based	O
commands	O
can	O
be	O
used	O
as	O
long	O
as	O
the	O
sequential	O
requirement	O
is	O
followed	O
on	O
host-managed	O
drives	O
.	O
</s>
<s>
Host-aware	O
or	O
device-managed	O
drives	O
are	O
marked	O
as	O
normal	O
block	O
devices	O
(	O
SCSI	B-Architecture
00h	O
)	O
,	O
so	O
they	O
can	O
be	O
recognized	O
as	O
a	O
normal	O
hard	B-Device
drive	I-Device
.	O
</s>
<s>
This	O
is	O
found	O
in	O
the	O
SCSI	B-Architecture
Block	O
Device	O
Characteristics	O
VPD	O
page	O
and	O
the	O
ATA	O
capabilities	O
log	O
page	O
.	O
</s>
<s>
Host-managed	O
drives	O
use	O
a	O
new	O
device	O
type	O
(	O
SCSI	B-Architecture
14h	O
)	O
.	O
</s>
<s>
The	O
zoned	O
interface	O
is	O
also	O
useful	O
for	O
flash	B-Device
storage	I-Device
.	O
</s>
<s>
ZNS	O
spec	O
has	O
been	O
released	O
by	O
the	O
NVM	B-Application
Express	I-Application
organization	O
.	O
</s>
<s>
The	O
higher	O
density	O
of	O
SMR	O
drives	O
,	O
combined	O
with	O
its	O
random-read	O
nature	O
,	O
fills	O
a	O
niche	O
between	O
the	O
sequential-access	O
tape	B-Architecture
storage	I-Architecture
and	O
the	O
random-access	O
conventional	O
hard	B-Device
drive	I-Device
storage	O
.	O
</s>
<s>
One	O
example	O
of	O
the	O
use	O
case	O
is	O
Dropbox	B-Application
's	O
Magic	O
Storage	O
system	O
,	O
which	O
runs	O
the	O
on-disk	O
extents	O
in	O
an	O
append-only	B-General_Concept
way	O
.	O
</s>
<s>
A	O
number	O
of	O
file	B-Application
systems	I-Application
in	O
Linux	B-Application
are	O
or	O
can	O
be	O
tuned	O
for	O
SMR	O
drives	O
:	O
</s>
<s>
F2FS	B-Application
,	O
originally	O
designed	O
for	O
flash	B-Device
media	I-Device
,	O
has	O
a	O
Zoned	O
Block	O
Device	O
(	O
ZBD	O
)	O
mode	O
.	O
</s>
<s>
Btrfs	B-Operating_System
had	O
ZBD	O
support	O
added	O
in	O
Linux	B-Application
kernel	O
5.12	O
,	O
and	O
it	O
already	O
writes	O
mostly	O
sequentially	O
due	O
to	O
the	O
CoW	O
nature	O
.	O
</s>
<s>
ext4	B-Application
can	O
be	O
experimentally	O
tuned	O
to	O
write	O
more	O
sequentially	O
.	O
</s>
<s>
Theodore	O
Ts'o	O
and	O
Abutalib	O
Aghayev	O
gave	O
a	O
talk	O
in	O
2017	O
on	O
their	O
ext4-lazy	O
.	O
</s>
<s>
For	O
other	O
filesystems	B-Application
,	O
the	O
Linux	B-Application
device	O
mapper	O
has	O
a	O
dm-zoned	O
target	O
that	O
maps	O
a	O
host-managed	O
drive	O
into	O
a	O
random-writable	O
drive	O
.	O
</s>
<s>
Linux	B-Application
kernels	O
since	O
4.10	O
can	O
perform	O
this	O
task	O
without	O
dm	O
.	O
</s>
<s>
In	O
addition	O
to	O
Linux	B-Application
,	O
FreeBSD	B-Operating_System
has	O
protocol-level	O
support	O
for	O
host-managed	O
SMR	O
drives	O
.	O
</s>
<s>
Adjusting	O
the	O
SMR/PMR	O
setting	O
helps	O
suit	O
the	O
drive	O
to	O
the	O
current	O
workload	O
of	O
"	O
hot	O
"	O
and	O
"	O
cold	O
"	O
data	O
.	O
</s>
