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 lat-
est kernel source code.
When no flags are given, -acdgkmnru is assumed.
-a Get/set sector count for filesystem read-ahead. This is used to improve perfor-
mance in sequential reads of large files, by prefetching additional blocks in
anticipation of them being needed by the running task. In the current kernel ver-
sion (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 drive.
-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 supported values include 0 to disable
32-bit I/O support, 1 to enable 32-bit data transfers, and 3 to enable 32-bit data
transfers 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 completely
shut down). The -S, -y, -Y, and -Z flags can be used to manipulate the IDE power
-d Disable/enable the "using_dma" flag for this drive. This option now works with
most combinations of drives and PCI interfaces which support DMA and which are
known to the IDE driver. It is also a good idea to use the appropriate -X option
in combination with -d1 to ensure that the drive itself is programmed for the cor-
rect DMA mode, although most BIOSs should do this for you at boot time. Using DMA
nearly always gives the best performance, with fast I/O throughput and low CPU
usage. But there are at least a few configurations of chipsets and drives for
which DMA 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 sectors by relocating them to "spare" sec-
tors reserved by the factory 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 sup-
ply 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 19/93).
-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 com-
bined 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
-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 there-
fore 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 neces-
sary 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 systems).
-K Set the drive's keep_features_over_reset flag. Setting this enables the drive to
retain the settings for -APSWXZ over a soft reset (as done during the error recov-
ery sequence). Not all drives support this feature.
-L Set the drive's doorlock flag. Setting this to will lock the door mechanism of
some removeable hard drives (eg. Syquest, ZIP, Jazz..), and setting it to maintains
the door locking mechanism automatically, depending on drive usage (locked whenever
a 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
-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 mod-
ern IDE hard drives, permitting the transfer of multiple sectors per I/O interrupt,
rather than the usual one sector per interrupt. When this feature is enabled, it
typically reduces operating system overhead for disk I/O by 30-50%. On many sys-
tems, 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 multi-
ple 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 Digital
recommends lower settings of 4 to 8 on many of their drives, due tiny (32kB) drive
buffers and non-optimized buffering 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 set-
tings. Under rare circumstances, such failures can result in massive filesystem
-M Get/set Automatic Acoustic Management (AAM) setting. Most modern harddisk drives
have the ability to speed down the head movements 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 lev-
els (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 supported by the drive. This feature
is supported in the kernel for only a few "known" chipsets, and even then the sup-
port 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 caution! This feature includes
zero protection for the unwary, and an unsuccessful outcome may result in severe
-P Set the maximum sector count for the drive's internal prefetch mechanism. Not all
drives support this feature.
-q Handle the next flag quietly, supressing normal output. This is useful for reduc-
ing screen clutter when running from /etc/rc.c/rc.local. Not applicable to the -i
or -v or -t or -T flags.
-Q Set tagged queue depth (1 or greater), or turn tagged queuing off (0). This only
works with the newer 2.5.xx (or later) kernels, and only with the few drives that
currently support it.
-r Get/set read-only flag for device. When set, write operations are not permitted on
-R Register an IDE interface. Dangerous. See the -U option for more information.
-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 spin-
dle motor to save power. Under such circumstances, the drive may take as long as
30 seconds 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 vendor-defined timeout, and 255 is interpreted as
21 minutes plus 15 seconds.
-T Perform timings of cache reads for benchmark and comparison purposes. For meaning-
ful 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 mem-
ory. This displays the speed of reading directly from the Linux buffer cache with-
out 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 incor-
porated into the result reported for the -t operation.
-t Perform timings of device reads for benchmark and comparison purposes. For mean-
ingful results, this operation should be repeated 2-3 times on an otherwise inac-
tive 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 measurement is an indication of how fast
the drive can sustain sequential data reads under Linux, without any filesystem
overhead. 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 responsiveness and eliminates "serial port overrun" errors. Use
this feature 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 particular, 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 feature of these interfaces (usu-
ally a BIOS/CMOS setting) provides a safe fix for the problem for use with earlier
-U Un-register an IDE interface. Dangerous. The companion for the -R option.
Intended for use with hardware made specifically for hot-swapping (very rare!).
Use with knowledge and extreme caution as this can easily hang or damage your sys-
tem. The hdparm source distribution includes a 'contrib' directory with some user-
donated scripts for hot-swapping on the UltraBay of a ThinkPad 600E. Use at your
-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 undeter-
minable; 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 necessary 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 multiword DMA, the value used is the desired DMA mode number
plus 32. for UltraDMA, the value is the desired UltraDMA mode number plus 64.
-y Force an IDE drive to immediately enter the low power consumption 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 consumption 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
-z Force a kernel re-read of the partition table of the specified device(s).
-Z Disable the automatic power-saving function of certain Seagate drives (ST3xxx mod-
els?), to prevent them from idling/spinning-down at inconvenient times.
As noted above, the -m sectcount and -u 1 options should be used with caution at first,
preferably on a read-only filesystem. Most drives work well with these features, but a
few drive/controller combinations are not 100% compatible. Filesystem corruption may
result. Backup everything before experimenting!
Some options (eg. -r for SCSI) may not work with old kernels as necessary ioctl()'s were
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 interfaces.
hdparm has been written by Mark Lord <email@example.com>, the primary developer and main-
tainer of the (E)IDE driver for Linux, with suggestions 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
AT Attachment Interface with Extensions (ATA-2), ANSI ASC X3T9.2 working draft, revision
2f, July 26, 1994.
AT Attachment with Packet Interface - 5 (ATA/ATAPI-5), T13-1321D working draft, revision
3, February 29, 2000.
AT Attachment with Packet Interface - 6 (ATA/ATAPI-6), T13-1410D working draft, revision
3b, February 26, 2002.
Western Digital Enhanced IDE Implementation Guide, by Western Digital Corporation, revi-
sion 5.0, November 10, 1993.
Enhanced Disk Drive Specification, by Phoenix Technologies Ltd., version 1.0, January 25,
Version 5.2 May 2002 HDPARM(8)