hdparm - get/set hard disk parameters
hdparm [ flags ] [device] ..
hdparm provides a command line interface to various hard disk ioctls
supported by the stock Linux ATA/IDE device driver subsystem. Some
options may work correctly only with the latest kernels. For best
results, compile hdparm with the include files from the latest kernel
When no flags are given, -acdgkmnru is assumed.
-a Get/set sector count for filesystem read-ahead. This is used to
improve performance in sequential reads of large files, by
prefetching additional blocks in anticipation of them being
needed by the running task. In the current kernel version
(2.0.10) this has a default setting of 8 sectors (4KB). This
value seems good for most purposes, but in a system where most
file accesses are random seeks, a smaller setting might provide
better performance. Also, many IDE drives also have a separate
built-in read-ahead function, which alleviates the need for a
filesystem read-ahead in many situations.
-A Disable/enable the IDE drive's read-lookahead feature (usually
ON by default).
-b Get/set bus state.
-B Set Advanced Power Management feature, if the drive supports it.
A low value means aggressive power management and a high value
means better performance. A value of 255 will disable apm on the
-c Query/enable (E)IDE 32-bit I/O support. A numeric parameter can
be used to enable/disable 32-bit I/O support: Currently sup-
ported values include 0 to disable 32-bit I/O support, 1 to
enable 32-bit data transfers, and 3 to enable 32-bit data trans-
fers with a special sync sequence required by many chipsets.
The value 3 works with nearly all 32-bit IDE chipsets, but
incurs slightly more overhead. Note that "32-bit" refers to
data transfers across a PCI or VLB bus to the interface card
only; all (E)IDE drives still have only a 16-bit connection over
the ribbon cable from the interface card.
-C Check the current IDE power mode status, which will always be
one of unknown (drive does not support this command),
active/idle (normal operation), standby (low power mode, drive
has spun down), or sleeping (lowest power mode, drive is com-
pletely shut down). The -S, -y, -Y, and -Z flags can be used to
manipulate the IDE power modes.
does not make much of a difference, or may even slow things down
(on really messed up hardware!). Your mileage may vary.
-D Enable/disable the on-drive defect management feature, whereby
the drive firmware tries to automatically manage defective sec-
tors by relocating them to "spare" sectors reserved by the fac-
tory for such.
-E Set cdrom speed. This is NOT necessary for regular operation,
as the drive will automatically switch speeds on its own. But
if you want to play with it, just supply a speed number after
the option, usually a number like 2 or 4.
-f Sync and flush the buffer cache for the device on exit. This
operation is also performed as part of the -t and -T timings.
-g Display the drive geometry (cylinders, heads, sectors), the size
(in sectors) of the device, and the starting offset (in sectors)
of the device from the beginning of the drive.
-h Display terse usage information (help).
-i Display the identification info that was obtained from the drive
at boot time, if available. This is a feature of modern IDE
drives, and may not be supported by older devices. The data
returned may or may not be current, depending on activity since
booting the system. However, the current multiple sector mode
count is always shown. For a more detailed interpretation of
the identification info, refer to AT Attachment Interface for
Disk Drives (ANSI ASC X3T9.2 working draft, revision 4a, April
-I Request identification info directly from the drive, which is
displayed in a new expanded format with considerably more detail
than with the older -i flag. There is a special "no seatbelts"
variation on this option, -Istdin which cannot be combined with
any other options, and which accepts a drive identification
block as standard input instead of using a /dev/hd* parameter.
The format of this block must be exactly the same as that found
in the /proc/ide/*/hd*/identify "files". This variation is
designed for use with "libraries" of drive identification infor-
mation, and can also be used on ATAPI drives which may give
media errors with the standard mechanism.
-k Get/set the keep_settings_over_reset flag for the drive. When
this flag is set, the driver will preserve the -dmu options over
a soft reset, (as done during the error recovery sequence).
This flag defaults to off, to prevent drive reset loops which
could be caused by combinations of -dmu settings. The -k flag
should therefore only be set after one has achieved confidence
in correct system operation with a chosen set of configuration
settings. In practice, all that is typically necessary to test
a configuration (prior to using -k) is to verify that the drive
can be read/written, and that no error logs (kernel messages)
are generated in the process (look in /var/adm/messages on most
filesystem is mounted). But on system shutdown, this can be a
nuisance if the root partition is on a removeable disk, since
the root partition is left mounted (read-only) after shutdown.
So, by using this command to unlock the door the root filesystem
is remounted read-only, one can then remove the cartridge from
the drive after shutdown.
-m Get/set sector count for multiple sector I/O on the drive. A
setting of 0 disables this feature. Multiple sector mode (aka
IDE Block Mode), is a feature of most modern IDE hard drives,
permitting the transfer of multiple sectors per I/O interrupt,
rather than the usual one sector per interrupt. When this fea-
ture is enabled, it typically reduces operating system overhead
for disk I/O by 30-50%. On many systems, it also provides
increased data throughput of anywhere from 5% to 50%. Some
drives, however (most notably the WD Caviar series), seem to run
slower with multiple mode enabled. Your mileage may vary. Most
drives support the minimum settings of 2, 4, 8, or 16 (sectors).
Larger settings may also be possible, depending on the drive. A
setting of 16 or 32 seems optimal on many systems. Western Dig-
ital recommends lower settings of 4 to 8 on many of their
drives, due tiny (32kB) drive buffers and non-optimized buffer-
ing algorithms. The -i flag can be used to find the maximum
setting supported by an installed drive (look for MaxMultSect in
the output). Some drives claim to support multiple mode, but
lose data at some settings. Under rare circumstances, such
failures can result in massive filesystem corruption.
-M Get/set Automatic Acoustic Management (AAM) setting. Most modern
harddisk drives have the ability to speed down the head move-
ments to reduce their noise output. The possible values are
between 0 and 254. 128 is the most quiet (and therefore slowest)
setting and 254 the fastest (and loudest). Some drives have
ownly two levels (quiet / fast), while others may have different
levels between 128 and 254. THIS FEATURE IS EXPERIMENTAL AND
NOT WELL TESTED. USE AT YOUR OWN RISK.
-n Get or set the "ignore write errors" flag in the driver. Do NOT
play with this without grokking the driver source code first.
-p Attempt to reprogram the IDE interface chipset for the specified
PIO mode, or attempt to auto-tune for the "best" PIO mode sup-
ported by the drive. This feature is supported in the kernel
for only a few "known" chipsets, and even then the support is
iffy at best. Some IDE chipsets are unable to alter the PIO
mode for a single drive, in which case this flag may cause the
PIO mode for both drives to be set. Many IDE chipsets support
either fewer or more than the standard six (0 to 5) PIO modes,
so the exact speed setting that is actually implemented will
vary by chipset/driver sophistication. Use with extreme cau-
tion! This feature includes zero protection for the unwary, and
an unsuccessful outcome may result in severe filesystem corrup-
-P Set the maximum sector count for the drive's internal prefetch
mechanism. Not all drives support this feature.
-r Get/set read-only flag for device. When set, write operations
are not permitted on the device.
-R Register an IDE interface. Dangerous. See the -U option for
-S Set the standby (spindown) timeout for the drive. This value is
used by the drive to determine how long to wait (with no disk
activity) before turning off the spindle motor to save power.
Under such circumstances, the drive may take as long as 30 sec-
onds to respond to a subsequent disk access, though most drives
are much quicker. The encoding of the timeout value is somewhat
peculiar. A value of zero means "off". Values from 1 to 240
specify multiples of 5 seconds, for timeouts from 5 seconds to
20 minutes. Values from 241 to 251 specify from 1 to 11 units
of 30 minutes, for timeouts from 30 minutes to 5.5 hours. A
value of 252 signifies a timeout of 21 minutes, 253 sets a ven-
dor-defined timeout, and 255 is interpreted as 21 minutes plus
-T Perform timings of cache reads for benchmark and comparison pur-
poses. For meaningful results, this operation should be
repeated 2-3 times on an otherwise inactive system (no other
active processes) with at least a couple of megabytes of free
memory. This displays the speed of reading directly from the
Linux buffer cache without disk access. This measurement is
essentially an indication of the throughput of the processor,
cache, and memory of the system under test. If the -t flag is
also specified, then a correction factor based on the outcome of
-T will be incorporated into the result reported for the -t
-t Perform timings of device reads for benchmark and comparison
purposes. For meaningful results, this operation should be
repeated 2-3 times on an otherwise inactive system (no other
active processes) with at least a couple of megabytes of free
memory. This displays the speed of reading through the buffer
cache to the disk without any prior caching of data. This mea-
surement is an indication of how fast the drive can sustain
sequential data reads under Linux, without any filesystem over-
head. To ensure accurate measurments, the buffer cache is
flushed during the processing of -t using the BLKFLSBUF ioctl.
If the -T flag is also specified, then a correction factor based
on the outcome of -T will be incorporated into the result
reported for the -t operation.
-u Get/set interrupt-unmask flag for the drive. A setting of 1
permits the driver to unmask other interrupts during processing
of a disk interrupt, which greatly improves Linux's responsive-
ness and eliminates "serial port overrun" errors. Use this fea-
ture with caution: some drive/controller combinations do not
tolerate the increased I/O latencies possible when this feature
is enabled, resulting in massive filesystem corruption. In par-
ticular, CMD-640B and RZ1000 (E)IDE interfaces can be unreliable
(due to a hardware flaw) when this option is used with kernel
versions earlier than 2.0.13. Disabling the IDE prefetch fea-
ture of these interfaces (usually a BIOS/CMOS setting) provides
-v Display all settings, except -i (same as -acdgkmnru for IDE, -gr
for SCSI or -adgr for XT). This is also the default behaviour
when no flags are specified.
-w Perform a device reset (DANGEROUS). Do NOT use this option. It
exists for unlikely situations where a reboot might otherwise be
required to get a confused drive back into a useable state.
-W Disable/enable the IDE drive's write-caching feature (default
state is undeterminable; manufacturer/model specific).
-x Tristate device for hotswap (DANGEROUS).
-X Set the IDE transfer mode for newer (E)IDE/ATA drives. This is
typically used in combination with -d1 when enabling DMA to/from
a drive on a supported interface chipset, where -X mdma2 is used
to select multiword DMA mode2 transfers and -X sdma1 is used to
select simple mode 1 DMA transfers. With systems which support
UltraDMA burst timings, -X udma2 is used to select UltraDMA
mode2 transfers (you'll need to prepare the chipset for UltraDMA
beforehand). Apart from that, use of this flag is seldom neces-
sary since most/all modern IDE drives default to their fastest
PIO transfer mode at power-on. Fiddling with this can be both
needless and risky. On drives which support alternate transfer
modes, -X can be used to switch the mode of the drive only.
Prior to changing the transfer mode, the IDE interface should be
jumpered or programmed (see -p flag) for the new mode setting to
prevent loss and/or corruption of data. Use this with extreme
caution! For the PIO (Programmed Input/Output) transfer modes
used by Linux, this value is simply the desired PIO mode number
plus 8. Thus, a value of 09 sets PIO mode1, 10 enables PIO
mode2, and 11 selects PIO mode3. Setting 00 restores the
drive's "default" PIO mode, and 01 disables IORDY. For multi-
word DMA, the value used is the desired DMA mode number plus 32.
for UltraDMA, the value is the desired UltraDMA mode number plus
-y Force an IDE drive to immediately enter the low power consump-
tion standby mode, usually causing it to spin down. The current
power mode status can be checked using the -C flag.
-Y Force an IDE drive to immediately enter the lowest power con-
sumption sleep mode, causing it to shut down completely. A hard
or soft reset is required before the drive can be accessed again
(the Linux IDE driver will automatically handle issuing a reset
if/when needed). The current power mode status can be checked
using the -C flag.
-z Force a kernel re-read of the partition table of the specified
-Z Disable the automatic power-saving function of certain Seagate
drives (ST3xxx models?), to prevent them from idling/spinning-
down at inconvenient times.
Although this utility is intended primarily for use with (E)IDE hard
disk devices, several of the options are also valid (and permitted) for
use with SCSI hard disk devices and MFM/RLL hard disks with XT inter-
hdparm has been written by Mark Lord <firstname.lastname@example.org>, the primary
developer and maintainer of the (E)IDE driver for Linux, with sugges-
tions from many netfolk.
The disable Seagate auto-powersaving code is courtesy of Tomi Leppikan-
AT Attachment Interface for Disk Drives, ANSI ASC X3T9.2 working draft,
revision 4a, April 19, 1993.
AT Attachment Interface with Extensions (ATA-2), ANSI ASC X3T9.2 work-
ing draft, revision 2f, July 26, 1994.
AT Attachment with Packet Interface - 5 (ATA/ATAPI-5), T13-1321D work-
ing draft, revision 3, February 29, 2000.
AT Attachment with Packet Interface - 6 (ATA/ATAPI-6), T13-1410D work-
ing draft, revision 3b, February 26, 2002.
Western Digital Enhanced IDE Implementation Guide, by Western Digital
Corporation, revision 5.0, November 10, 1993.
Enhanced Disk Drive Specification, by Phoenix Technologies Ltd., ver-
sion 1.0, January 25, 1994.
Version 5.2 May 2002 hdparm(8)