最近需要测试数据库的性能，需要关闭磁盘的写缓存，因此记录下 hdparm 命令的使用方法。
Linux下的hdparm（英文全称：hard disk parameters）命令，主要用来查看硬盘的相关信息或对硬盘进行测速、优化、修改硬盘相关参数设定。它提供了一个命令行的接口用于读取和设置IDE或SCSI硬盘参数。
若没有安装hdparm ，可以通过sudo yum install hdparm 来安装。
其对应的参数如下：
hdparm [options] ...[device]...
hdparm [参数]...[设备]...
Options:
-a Get/set fs readahead
-A Get/set the drive look-ahead flag (0/1)
-b Get/set bus state (0 == off, 1 == on, 2 == tristate)
-B Set Advanced Power Management setting (1-255)
-c Get/set IDE 32-bit IO setting
-C Check drive power mode status
-d Get/set using_dma flag
-D Enable/disable drive defect management
-E Set cd/dvd drive speed
-f Flush buffer cache for device on exit
-F Flush drive write cache
-g Display drive geometry
-h Display terse usage information
-H Read temperature from drive (Hitachi only)
-i Display drive identification
-I Detailed/current information directly from drive
-J Get/set Western DIgital "Idle3" timeout for a WDC "Green" drive (DANGEROUS)
-k Get/set keep_settings_over_reset flag (0/1)
-K Set drive keep_features_over_reset flag (0/1)
-L Set drive doorlock (0/1) (removable harddisks only)
-m Get/set multiple sector count
-M Get/set acoustic management (0-254, 128: quiet, 254: fast)
-n Get/set ignore-write-errors flag (0/1)
-N Get/set max visible number of sectors (HPA) (VERY DANGEROUS)
-p Set PIO mode on IDE interface chipset (0,1,2,3,4,...)
-P Set drive prefetch count
-q Change next setting quietly
-Q Get/set DMA queue_depth (if supported)
-r Get/set device readonly flag (DANGEROUS to set)
-R Get/set device write-read-verify flag
-s Set power-up in standby flag (0/1) (DANGEROUS)
-S Set standby (spindown) timeout
-t Perform device read timings
-T Perform cache read timings
-u Get/set unmaskirq flag (0/1)
-U Obsolete
-v Use defaults; same as -acdgkmur for IDE drives
-V Display program version and exit immediately
-w Perform device reset (DANGEROUS)
-W Get/set drive write-caching flag (0/1)
-x Obsolete
-X Set IDE xfer mode (DANGEROUS)
-y Put drive in standby mode
-Y Put drive to sleep
-z Re-read partition table
-Z Disable Seagate auto-powersaving mode
--dco-freeze Freeze/lock current device configuration until next power cycle
--dco-identify Read/dump device configuration identify data
--dco-restore Reset device configuration back to factory defaults
--direct Use O_DIRECT to bypass page cache for timings
--drq-hsm-error Crash system with a "stuck DRQ" error (VERY DANGEROUS)
--fallocate Create a file without writing data to disk
--fibmap Show device extents (and fragmentation) for a file
--fwdownload Download firmware file to drive (EXTREMELY DANGEROUS)
--fwdownload-mode3 Download firmware using min-size segments (EXTREMELY DANGEROUS)
--fwdownload-mode3-max Download firmware using max-size segments (EXTREMELY DANGEROUS)
--fwdownload-mode7 Download firmware using a single segment (EXTREMELY DANGEROUS)
--idle-immediate Idle drive immediately
--idle-unload Idle immediately and unload heads
--Istdin Read identify data from stdin as ASCII hex
--Istdout Write identify data to stdout as ASCII hex
--make-bad-sector Deliberately corrupt a sector directly on the media (VERY DANGEROUS)
--offset use with -t, to begin timings at given offset (in GiB) from start of drive
--prefer-ata12 Use 12-byte (instead of 16-byte) SAT commands when possible
--read-sector Read and dump (in hex) a sector directly from the media
--repair-sector Alias for the --write-sector option (VERY DANGEROUS)
--security-help Display help for ATA security commands
--trim-sector-ranges Tell SSD firmware to discard unneeded data sectors: lba:count ..
--trim-sector-ranges-stdin Same as above, but reads lba:count pairs from stdin
--verbose Display extra diagnostics from some commands
--write-sector Repair/overwrite a (possibly bad) sector directly on the media (VERY DANGEROUS)
选项说明：
-a<快取分区>：设定读取文件时，预先存入块区的分区数，若不加上<快取分区>选项，则显示目前的设定；
-A<0或1>：启动或关闭读取文件时的快取功能；
-c<I/O模式>：设定IDE32位I/O模式；
-C：检测IDE硬盘的电源管理模式；
-d<0或1>：设定磁盘的DMA模式；
-f：将内存缓冲区的数据写入硬盘，并清除缓冲区；
-g：显示硬盘的磁轨，磁头，磁区等参数；
-h：显示帮助；
-i：显示硬盘的硬件规格信息，这些信息是在开机时由硬盘本身所提供；
-I：直接读取硬盘所提供的硬件规格信息；
-k<0或1>：重设硬盘时，保留-dmu参数的设定；
-K<0或1>：重设硬盘时，保留-APSWXZ参数的设定；
-m<磁区数>：设定硬盘多重分区存取的分区数；
-n<0或1>：忽略硬盘写入时所发生的错误；
-p<PIO模式>：设定硬盘的PIO模式；
-P<磁区数>：设定硬盘内部快取的分区数；
-q:在执行后续的参数时，不在屏幕上显示任何信息；
-r<0或1>:设定硬盘的读写模式；
-S<时间>:设定硬盘进入省电模式前的等待时间；
-t;评估硬盘的读取效率；
-T：评估硬盘缓存的读取速度；
-u<0或1>：在硬盘存取时，允许其他中断要求同时执行；
-v：显示硬盘的相关设定；
-w<0或1>：设定硬盘的写入快取；
-X<传输模式>：设定硬盘的传输模式；
-y：使IDE硬盘进入省电模式；
-Y：使IDE硬盘进入睡眠模式；
-Z：关闭某些Seagate硬盘的自动省电功能。用来查看硬盘的相关信息或对硬盘进行测速、优化、修改硬盘相关参数设定。
用法如下：
显示硬盘的相关设置
# hdparm /dev/vda
/dev/vda:
HDIO_DRIVE_CMD(identify) failed: Inappropriate ioctl for device
readonly = 0 (off)
readahead = 8192 (on)
geometry = 104025/16/63, sectors = 104857600, start = 0显示硬盘的柱面、磁头、扇区数
# hdparm -g /dev/vda
/dev/vda:
geometry = 104025/16/63, sectors = 104857600, start = 0
#其中：
geometry = 104025［柱面数］/16［磁头数］/63［扇区数］, sectors = 104857600［总扇区数］, start = 0［起始扇区数］评估硬盘的读取效率
# hdparm -t /dev/vda
/dev/vda:
Timing buffered disk reads: 290 MB in 3.15 seconds = 92.08 MB/sec评估硬盘缓存的读取速度
# hdparm -T /dev/vda
/dev/vda:
Timing cached reads: 20508 MB in 2.00 seconds = 10267.18 MB/sec检测硬盘的电源管理模式
# hdparm -C /dev/vda
/dev/vda:
drive state is: unknown查看并设置硬盘多重扇区存取的扇区数，以增进硬盘的存取效率
#查看
# hdparm -m /dev/vda
#设置
# hdparm -m 8 /dev/vda读取硬盘所提供的硬件规格信息
#hdparm -I /dev/vda将内存缓冲区的数据写入硬盘，并清空缓冲区
# hdparm -f /dev/vda查看当前硬盘写Cache状态：
hdparm -W /dev/sda关闭硬盘的写Cache
hdparm -W 0 /dev/sda打开硬盘的写Cache
hdparm -W 1 /dev/sda对于硬盘较多，可以使用linux系统中的for循环结构来快速实现，例：
for dev in a b c d e f g h i g k l m n o..z;do hdparm -W 0(1) /dev/&dev;done。
