hdparm 命令使用;关闭硬盘 HDD cache; 硬盘读写性能测试；

hdparm -W  /dev/sdh # 查看写缓存状态；
hdparm -W  0 /dev/sdh # 关闭Cache,保证数据强一致性；放置断电时数据未落盘；
hdparm -W  1 /dev/sdh # 打开

查看磁盘信息：
fdisk -l  /dev/sdh
hdparm /dev/sdh
评估磁盘读取速度：
hdparm -t /dev/sdh
评估磁盘缓存读取速度：
hdparm -T /dev/sdh
直接测试硬盘的读性能(绕过内核页缓存)：
hdparm -tT --direct /dev/sdh
顺序写测试：
time -p  bash -c "dd if=/dev/urandom of=./dd.log bs=1M count=50000"
随机写测试：

hdparm -h

hdparm - get/set hard disk parameters - version v9.43, by Mark Lord.

Usage:  hdparm  [options] [device ...]

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)