linux系统中ssd当块设备缓存 | 您所在的位置:网站首页 › 固态硬盘当缓存盘 › linux系统中ssd当块设备缓存 |
原理 写操作先缓存到ssd硬盘上,然后通过一定策略写到普通硬盘上; 读操作热点数据可以缓存到ssd硬盘上,提高读取数据的速度。 软件 ssd 缓存开源软件主要有bcache ,flashcache bcache 需要编译最新的内核,要求比较高,配置比较复杂,目前主要用于测试环境; flashcache 是facebook内部使用的ssd cache软件,开源出来供大家使用,目前有人编译出rhel6的rpm包,在centos6上可以直接安装使用。 本次初步测试了flashcache 测试环境 sdc为 ssd 硬盘 160G*4 raid 10 用fio测试 4k 写iops为 5433 sdb为 普通sas硬盘 146G*2 raid 1 用fio测试 4k 写iops为 447 初步简单测试结果: 4k 随机写可以达到 5014 4k随机读可以达到45874 flashcache 安装配置方法 安装 rpm --import http://elrepo.org/RPM-GPG-KEY-elrepo.org rpm -Uvh http://elrepo.org/elrepo-release-6-5.el6.elrepo.noarch.rpm yum install flashcache-utils kmod-flashcache 配置: 用sdc 做sdb的缓存 flashcache_create -p back cachedev /dev/sdc /dev/sdb cachedev cachedev, ssd_devname /dev/sdc, disk_devname /dev/sdb cache mode WRITE_BACK block_size 8, md_block_size 8, cache_size 0 Flashcache metadata will use 1192MB of your 24016MB main memory 可以用3种方式: Writethrough - safest, all writes are cached to ssd but also written to disk immediately. If your ssd has slower write performance than your disk (likely for early generation SSDs purchased in 2008-2010), this may limit your system write performance. All disk reads are cached (tunable). 数据同时写到ssd和普通硬盘 Writearound - again, very safe, writes are not written to ssd but directly to disk. Disk blocks will only be cached after they are read. All disk reads are cached (tunable). 数据同时绕过ssd,直接写到普通硬盘 Writeback - fastest but less safe. Writes only go to the ssd initially, and based on various policies are written to disk later. All disk reads are cached (tunable). 数据先写到ssd,随后写到普通硬盘 查看 flashstat ====================================================================================================== Flashstat: a tool for flashcache status per second Author : NinGoo([email protected]) Version : 0.3 ====================================================================================================== SSD Device: /dev/sdc Disk Device: /dev/sdb Cache Mode: WRITE_BACK Capacity: 303998M Block Size: 4K Meta Block Size: 4096b Total Blocks: 77823488 Cached Blocks: 9 Cached Percent: 0 Set Numbers: 512 Dirty Blocks: 0 Dirty Percent: 0 cache_all: 1 reclaim_policy: FIFO dirty_thresh_pct: 20 max_clean_ios_set: 2 max_clean_ios_total: 4 skip_seq_thresh: 0K ====================================================================================================== time read/s write/s diskr/s diskw/s ssdr/s ssdw/s uread/s uwrit/s metaw/s clean/s repl/s wrepl/s hit% whit% dwhit% 03-13 14:51:20 0 0 0 0 0 0 0 0 0 0 0 0 0|10 0|0 0|0 fdisk -l /dev/mapper/cachedev 可以看到一个设备 Disk /dev/mapper/cachedev: 146.8 GB, 146778685440 bytes 255 heads, 63 sectors/track, 17844 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x0002da0a Device Boot Start End Blocks Id System 使用: 可以当一个块设备来使用,划分vg lv pvcreate /dev/mapper/cachedev Physical volume "/dev/mapper/cachedev" successfully created vgcreate ssdcachetest /dev/mapper/cachedev Volume group "ssdcachetest" successfully created lvcreate -L 100G -n ssdcache_test_lv1 ssdcachetest Logical volume "ssdcache_test_lv1" created 删除 dmsetup remove cachedev flashcache_destroy /dev/sdc |
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