Manpage of HDPARM


Section: Maintenance Commands (8)
Updated: November 2001
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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 source code.  


When no flags are given, -acdgkmnru is assumed.
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.
Disable/enable the IDE drive's read-lookahead feature (usually ON by default).
Get/set bus state.
Get setting of Advanced Power Management feature, if the drive supports it.
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.
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 modes.
Disable/enable the "using_dma" flag for this drive. This option only works with a few combinations of drives and interfaces which support DMA and which are known to the IDE driver (and with all supported XT interfaces). In particular, the Intel Triton chipset is supported for bus-mastered DMA operation with many drives (experimental). It is also a good idea to use the -X34 option in combination with -d1 to ensure that the drive itself is programmed for multiword DMA mode2. Using DMA does not necessarily provide any improvement in throughput or system performance, but many folks swear by it. Your mileage may vary.
Enable/disable the on-drive defect management feature, whereby the drive firmware tries to automatically manage defective sectors by relocating them to "spare" sectors reserved by the factory for such.
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.
Sync and flush the buffer cache for the device on exit. This operation is also performed as part of the -t and -T timings.
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.
Display terse usage information (help).
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).
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.
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 systems).
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 recovery sequence). Not all drives support this feature.
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 after shutdown.
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 feature 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 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 settings. Under rare circumstances, such failures can result in massive filesystem corruption.
Get or set the "ignore write errors" flag in the driver. Do NOT play with this without grokking the driver source code first.
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 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 caution! This feature includes zero protection for the unwary, and an unsuccessful outcome may result in severe filesystem corruption!
Set the maximum sector count for the drive's internal prefetch mechanism. Not all drives support this feature.
Handle the next flag quietly, supressing normal output. This is useful for reducing screen clutter when running from /etc/rc.c/rc.local. Not applicable to the -i or -v or -t or -T flags.
Get/set read-only flag for device. When set, write operations are not permitted on the device.
Register an IDE interface. Dangerous. See the -U option for more information.
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 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.
Perform timings of cache 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 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 operation.
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 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.
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 (usually a BIOS/CMOS setting) provides a safe fix for the problem for use with earlier kernels.
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 system. 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 own risk.
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. -TP -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.
Disable/enable the IDE drive's write-caching feature (default state is undeterminable; manufacturer/model specific).
Set the IDE transfer mode for newer (E)IDE/ATA2 drives. This is typically used in combination with -d1 when enabling DMA to/from a drive on a supported interface chipset (such as the Intel 430FX Triton), where -X34 is used to select multiword DMA mode2 transfers. With systems which support UltraDMA burst timings, -X66 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.
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.
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 flag.
Disable the automatic power-saving function of certain Seagate drives (ST3xxx models?), 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 not supported.

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 <>, the primary developer and maintainer of the (E)IDE driver for Linux, with suggestions from many netfolk.

The disable Seagate auto-powersaving code is courtesy of Tomi Leppikangas(  


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 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.

Western Digital Enhanced IDE Implementation Guide, by Western Digital Corporation, revision 5.0, November 10, 1993.

Enhanced Disk Drive Specification, by Phoenix Technologies Ltd., version 1.0, January 25, 1994.




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