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RAID卡的缓存与磁盘自带的缓存的关系
RAID卡是否有(启用)缓存对“随机读写”性能有巨大的影响。中高端的RAID卡都有缓存(价格也高)。 那么RAID卡的缓存与磁盘自带的缓存是如何设置的?
戴尔服务器的perc H710 RAID卡有512M缓存,并带电池。 建立阵列的时候(raid5),关于RAID卡缓存的默认选项是: 读取策略:自适应 写策略:回写 磁盘高速缓存策略:禁用
属性解释: 读取策略:一般要启用,采用预读取策略,可提高“随机读取”性能。第二次读取相同数据时可以命中缓存。 写策略: 一般要启用“回写”,操作的是RAID卡上的缓存。 写入数据时先写入到缓存就算写入成功了,然后RAID卡控制器再把多个写IO合并为一个写IO一次性写入磁盘,提高“随机写入”的性能。 因为RAID卡带电池,机房停电时,电池可给缓存供电72小时。缓存中的数据不会丢失。 另外,如果没有给缓存接电池,默认“写缓存”是不被启用的(除非强行设定为“没有电池也启用写缓存”)。
磁盘高速缓存策略: 操作的是磁盘自带的高速缓存。 做RAID时,一般要禁用,防止机房停电时磁盘自带缓存中的数据丢失。磁盘可不带电池。 RAID卡控制器可控制磁盘自带的缓存是否启用。 家用台试机(未使用RAID卡)在windows操作系统中有选项可以控制磁盘自带的缓存是否启用(默认启用)。
Windows如何开启、关闭磁盘写缓存
打开磁盘写入缓存可以提高操作系统的性能 ;但是,突然停电时它可能导致信息的丢失。下面介绍如何启用磁盘写入缓存打开或关闭。 打开或关闭磁盘写入缓存: 1、用鼠标右键单击我的电脑,然后单击属性 2、单击硬件选项卡,然后单击设备管理器 3、扩展磁盘驱动器 4、用鼠标右键单击您要在其打开磁盘写入缓存打开或关闭,的驱动器,然后单击属性 5、单击策略选项卡。 6、单击以选中或清除相应的启用写入缓存在磁盘上复选框。 7、单击确定
Linux如何开启、关闭硬盘写缓存(Write Cache)
在Linux中,有时我们希望打开或关闭硬盘写缓存(Write Cache),此时可以用hdparm命令来实现。
建议下载最新hdparm版本,网址为:http://sourceforge.net/projects/hdparm/ 下载自行安装 CentOS 5.4 默认带的hdparm是6.6版本,要升级一下。yum update hdparm,试了好几个yum源,最新的都是6.6,不能通过yum升级。
hdparm的改变是个临时的状态,下次再次启动Linux系统的时候hdparm将会消失。所以要想永久的保存修改后的信息,就必须把修改后的参数和数据写入/etc/rc.d/rc.local或/etc/rc.local文档,甚至比启动过程要早运行的程式中。
安装 hdparm 用以下命令安装 hdparm: make && make install
注意在默认情况下, hdparm 是安装在 /sbin 因为一些系统可呢能需要它在启动时在/usr被连接前. 如果你想把 hdparm 安装在 /usr下, 那么替换上面的命令为下面这个: make && make binprefix=/usr install
测试服务器磁盘读写速度:hpparm -T -t /dev/sdx -T 表示不读取磁盘,直接从Linux缓存读取数据的速度 -t 表示不使用预先的数据缓冲从磁盘连续读取的速度 /dev/sdx是设备名
查看当前硬盘写Cache状态 root@ubuntu:~/hdparm-9.37# hdparm -W /dev/sda
关闭硬盘的写Cache root@ubuntu:~/hdparm-9.37# hdparm -W 0 /dev/sda
打开硬盘的写Cache root@ubuntu:~/hdparm-9.37# hdparm -W 1 /dev/sda
hdparm的参数参数说明: root@ubuntu:~/hdparm-9.37# ./hdparm -h hdparm – get/set hard disk parameters – version v9.37, 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 -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 Obsolete -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 –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)
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