腳本之家服務器常用軟件

快捷導航

在Linux系統(tǒng)中將SSD當塊設備緩存的方法

xiaoli110的BLOG 發(fā)布時間：2015-07-02 15:58:17 作者：佚名

我要評論

這篇文章主要介紹了在Linux系統(tǒng)中將SSD當塊設備緩存的方法,主要是將SSD作為內存和HDD中間的過度緩存設備,需要的朋友可以參考下

原理

寫操作先緩存到ssd硬盤上，然后通過一定策略寫到普通硬盤上；

讀操作熱點數據可以緩存到ssd硬盤上，提高讀取數據的速度。

軟件 ssd 緩存開源軟件主要有bcache ，flashcache

bcache 需要編譯最新的內核，要求比較高，配置比較復雜，目前主要用于測試環(huán)境；

flashcache 是facebook內部使用的ssd cache軟件，開源出來供大家使用，目前有人編譯出rhel6的rpm包，在centos6上可以直接安裝使用。

本次初步測試了flashcache

測試環(huán)境

sdc為 ssd 硬盤 160G*4 raid 10 用fio測試 4k 寫iops為 5433

sdb為普通sas硬盤 146G*2 raid 1 用fio測試 4k 寫iops為 447

初步簡單測試結果：

4k 隨機寫可以達到 5014

4k隨機讀可以達到45874

flashcache 安裝配置方法

安裝

復制代碼

代碼如下:

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的緩存

復制代碼

代碼如下:

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種方式：

復制代碼

代碼如下:

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).

數據同時寫到ssd和普通硬盤

復制代碼

代碼如下:

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).

數據同時繞過ssd，直接寫到普通硬盤

復制代碼

代碼如下:

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).

數據先寫到ssd，隨后寫到普通硬盤

查看

flashstat

======================================================================================================

Flashstat: a tool for flashcache status per second

Author : NinGoo(seaman.ning@gmail.com)

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

復制代碼

代碼如下:

fdisk -l /dev/mapper/cachedev

可以看到一個設備

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：

可以當一個塊設備來使用，劃分vg lv

復制代碼

代碼如下:

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

刪除

復制代碼

代碼如下:

dmsetup remove cachedev flashcache_destroy /dev/sdc