ceph 调优
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一、关于内核调优 /etc/sysctl.conf
	# Controls IP packet forwarding
	net.ipv4.ip_forward = 0

	# Controls source route verification
	net.ipv4.conf.default.rp_filter = 1

	# Do not accept source routing
	net.ipv4.conf.default.accept_source_route = 0

	# Controls the System Request debugging functionality of the kernel
	kernel.sysrq = 0

	# Controls whether core dumps will append the PID to the core filename.
	# Useful for debugging multi-threaded applications.
	kernel.core_uses_pid = 1

	# disable TIME_WAIT.. wait ..
	net.ipv4.tcp_tw_recycle = 1
	net.ipv4.tcp_tw_reuse = 1

	# Controls the use of TCP syncookies
	net.ipv4.tcp_syncookies = 0

	# Controls the maximum size of a message, in bytes
	kernel.msgmnb = 65536

	# Controls the default maxmimum size of a mesage queue
	kernel.msgmax = 65536

	# Controls the maximum shared segment size, in bytes
	kernel.shmmax = 68719476736

	# Controls the maximum number of shared memory segments, in pages
	kernel.shmall = 4294967296

二、巨型帧调整
	如果交换机支持巨型帧，则较大的MTU大小会有所帮助。我们的测试显示 9000 MTU改善了顺序读/写性能。

三、硬盘配置
	Read_ahead是Linux操作系统中使用的文件预取技术。它是一个系统调用，它将文件的内容加载到页面缓存中。随后访问文件时，其内容将从物理内
	存而不是从磁盘读取，这要快得多。readahead是Linux系统API，是提示（hint）系统将指定文件的某区域预读进页缓存， 便于接下来对该区域进
	行读域进行读取时，不会因缺页（page fault）而阻塞。
		echo 512 > /sys/block/sda/queue/read_ahead_kb

四、参考文档
	http://tracker.ceph.com/projects/ceph/wiki/Tuning_for_All_Flash_Deployments#Sample-Ceph-Vendor-Solutions
	
	
kernel.sched_min_granularity_ns = 10000000
kernel.sched_wakeup_granularity_ns = 15000000
fs.aio-max-nr=1048576
kernel.pid_max=4194303
fs.file-max=26234859
vm.zone_reclaim_mode=0
vm.swappiness=1
vm.dirty_ratio = 10
vm.dirty_background_ratio = 5
net.ipv4.tcp_rmem=4096 87380 134217728
net.ipv4.tcp_wmem=4096 65536 134217728
net.core.rmem_max=268435456
net.core.wmem_max=268435456
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_fin_timeout = 10
net.ipv4.tcp_slow_start_after_idle = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.tcp_mtu_probing = 1
net.ipv4.tcp_timestamps = 0
net.core.netdev_max_backlog = 50000
net.ipv4.tcp_max_syn_backlog = 30000
net.ipv4.tcp_max_tw_buckets = 2000000
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