这里不介绍几种调度的原理，个人知识深度有限，其次，是基于服务器做维护调优，只要知道对我db服务器有利，即可。

一、I/O调度器的选择
目前主流Linux发行版本使用三种I/O调度器：DeadLine、CFQ、NOOP：
Deadline适用于大多数环境,特别是写入较多的文件服务器，从原理上看，DeadLine是一种以提高机械硬盘吞吐量为思考出发点的调度算法，尽量保证在有I/O请求达到最终期限的时候进行调度，非常适合业务比较单一并且I/O压力比较重的业务，比如Web服务器，数据库应用等。
CFQ 为所有进程分配等量的带宽,适用于有大量进程的多用户系统，CFQ是一种比较通用的调度算法，它是一种以进程为出发点考虑的调度算法，保证大家尽量公平,为所有进程分配等量的带宽,适合于桌面多任务及多媒体应用。
NOOP 对于闪存设备和嵌入式系统是最好的选择。对于固态硬盘来说使用NOOP是最好的，DeadLine次之，而CFQ效率最低。

二、查看Linux系统的 I/O调度器
查看Linux系统的I/O调度器一般分成两个部分，一个是查看Linux系统整体使用的I/O调度器，另一个是查看某磁盘使用的I/O调度器。

2.1 查看当前系统支持的I/O调度器，使用如下命令：

[root@localhost ~]# dmesg | grep -i scheduler
io scheduler noop registered
io scheduler anticipatory registered
io scheduler deadline registered
io scheduler cfq registered (default)

显示当前使用的调度器是cfq，就是括号括起来的那一个。

2.2 查看某块硬盘的IO调度算法I/O调度器，使用如下命令：

[root@localhost ~]# cat /sys/block/dm-1/queue/scheduler <<<<<<<这个block设备是通过sda 通过lvm虚拟化而来,所以只需关注sda盘即可
none
# cat /sys/block/sda/queue/scheduler
noop deadline [cfq]

显示当前使用的调度器是cfq，就是括号括起来的那一个。

三、修改Linux系统的 I/O调度器
修改Linux系统的 I/O调度器有三种方法，分别是使用shell命令、使用grubby命令或者修改grub配置文件。下面依次介绍：

Linux下更改的I/O调度器很简单。不需要更新内核，可以使用shell命令修改：
3.1 查使用shell命令
#echo noop > /sys/block/sdb/queue/scheduler
把noop设置为一个磁盘的I/O调度器，你可以随时更改而无需重启计算机。
永久修改默认的I/O调度器
使用shell命令修改I/O调度器，只是临时修改，系统重启后，修改的调度器就会失效，要想修改默认的调度器，有两种方法使用grubby命令或者直接编辑grub配置文件。

3.2 使用grubby命令

例如需要把I/O调度器从cfq调整成 DeadLine ，命令如下：
# grubby –grub –update-kernel=ALL –args=”elevator=deadline”
通过设置内核加载参数, 这样当机器重启的时候，系统自动把所有设备的 I/O调度器变成 DeadLine 。

3.3 使用编辑器修改配置文件
修改内核引导参数,加入elevator=调度程序名

vi /boot/grub/menu.lst
更改到如下内容:
kernel /boot/vmlinuz-2.6.32-431.el6.x86_64 ro root=LABEL=/ elevator=deadline rhgb quiet

Linux I/O调度器是 Linux 内核中的一个组成部分，用户可以通过根据不同的存储器来设置 Linux I/O 调度器从而达到优化系统性能。

resize2fs: Permission denied to resize filesystem

linux 下lvm扩容后，进行resize2fs进行容量的生效时，发现权限拒绝；通过查看卷的权限，连接等，都没有问题；

[root@trsen /]# strace -f resize2fs /dev/mapper/vgtrsen-u02
execve("/sbin/resize2fs", ["resize2fs", "/dev/mapper/vgtrsen-u02"], [/* 26 vars */]) = 0
brk(0) = 0x25a3000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75e6000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=68514, ...}) = 0
mmap(NULL, 68514, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fa1c75d5000
close(3) = 0
open("/lib64/libe2p.so.2", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200\37\200\3522\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=34904, ...}) = 0
mmap(0x32ea800000, 2128240, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x32ea800000
mprotect(0x32ea806000, 2097152, PROT_NONE) = 0
mmap(0x32eaa06000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x32eaa06000
close(3) = 0
open("/lib64/libext2fs.so.2", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\342\200\3512\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=283400, ...}) = 0
mmap(0x32e9800000, 2376760, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x32e9800000
mprotect(0x32e9843000, 2093056, PROT_NONE) = 0
mmap(0x32e9a42000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x42000) = 0x32e9a42000
close(3) = 0
open("/lib64/libcom_err.so.2", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\20\24@\3672\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=17256, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75d4000
mmap(0x32f7400000, 2109904, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x32f7400000
mprotect(0x32f7403000, 2093056, PROT_NONE) = 0
mmap(0x32f7602000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x32f7602000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0000\356\301\3512\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1930416, ...}) = 0
mmap(0x32e9c00000, 3750184, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x32e9c00000
mprotect(0x32e9d8a000, 2097152, PROT_NONE) = 0
mmap(0x32e9f8a000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x32e9f8a000
mmap(0x32e9f90000, 14632, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x32e9f90000
close(3) = 0
open("/lib64/libpthread.so.0", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0000^\0\3522\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=146592, ...}) = 0
mmap(0x32ea000000, 2212848, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x32ea000000
mprotect(0x32ea017000, 2097152, PROT_NONE) = 0
mmap(0x32ea217000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x17000) = 0x32ea217000
mmap(0x32ea219000, 13296, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x32ea219000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75d3000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75d1000
arch_prctl(ARCH_SET_FS, 0x7fa1c75d1720) = 0
mprotect(0x60a000, 4096, PROT_READ) = 0
mprotect(0x32eaa06000, 4096, PROT_READ) = 0
mprotect(0x32e9a42000, 4096, PROT_READ) = 0
mprotect(0x32f7602000, 4096, PROT_READ) = 0
mprotect(0x32e9f8a000, 16384, PROT_READ) = 0
mprotect(0x32ea217000, 4096, PROT_READ) = 0
mprotect(0x32e9620000, 4096, PROT_READ) = 0
munmap(0x7fa1c75d5000, 68514) = 0
set_tid_address(0x7fa1c75d19f0) = 12343
set_robust_list(0x7fa1c75d1a00, 24) = 0
futex(0x7ffd27f5ef4c, FUTEX_WAKE_PRIVATE, 1) = 0
futex(0x7ffd27f5ef4c, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 1, NULL, 7fa1c75d1720) = -1 EAGAIN (Resource temporarily unavailable)
rt_sigaction(SIGRTMIN, {0x32ea005cb0, [], SA_RESTORER|SA_SIGINFO, 0x32ea00f7e0}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {0x32ea005d40, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x32ea00f7e0}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
brk(0) = 0x25a3000
brk(0x25c4000) = 0x25c4000
open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=99174448, ...}) = 0
mmap(NULL, 99174448, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fa1c173c000
close(3) = 0
write(2, "resize2fs 1.43-WIP (20-Jun-2013)"..., 33resize2fs 1.43-WIP (20-Jun-2013)
) = 33
stat("/dev/mapper/vgtrsen-u02", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 3), ...}) = 0
open("/proc/swaps", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75e5000
read(3, "Filename\t\t\t\tType\t\tSize\tUsed\tPrio"..., 1024) = 161
stat("/dev/dm-1", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 1), ...}) = 0
stat("/swap1", {st_mode=S_IFREG|0644, st_size=21474836480, ...}) = 0
read(3, "", 1024) = 0
close(3) = 0
munmap(0x7fa1c75e5000, 4096) = 0
open("/proc/mounts", O_RDONLY|O_CLOEXEC) = 3
stat("/dev/mapper/vgtrsen-u02", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 3), ...}) = 0
futex(0x32e9f91040, FUTEX_WAKE_PRIVATE, 2147483647) = 0
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75e5000
read(3, "proc /proc proc rw,relatime 0 0\n"..., 1024) = 835
stat("/dev/mapper/vg_hpdpre-lv_root", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 0), ...}) = 0
stat("/dev/sda1", {st_mode=S_IFBLK|0660, st_rdev=makedev(8, 1), ...}) = 0
stat("/dev/mapper/vg_hpdpre-lv_home", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 4), ...}) = 0
stat("/dev/mapper/vgtrsen-u01", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 2), ...}) = 0
stat("/etc/auto.misc", {st_mode=S_IFREG|0644, st_size=524, ...}) = 0
stat("/u02", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
close(3) = 0
munmap(0x7fa1c75e5000, 4096) = 0
stat("/dev/mapper/vgtrsen-u02", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 3), ...}) = 0
open("/dev/mapper/vgtrsen-u02", O_RDONLY|O_EXCL) = -1 EBUSY (Device or resource busy)
open("/dev/mapper/vgtrsen-u02", O_RDWR) = 3
fstat(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 3), ...}) = 0
close(3) = 0
open("/dev/mapper/vgtrsen-u02", O_RDONLY) = 3
stat("/dev/mapper/vgtrsen-u02", {st_mode=S_IFBLK|0660, st_rdev=makedev(251, 3), ...}) = 0
ioctl(3, BLKDISCARDZEROES, 0) = 0
lseek(3, 1024, SEEK_SET) = 1024
read(3, "\0pT\16\0004\243r\201N\177\5-\372.\7UbT\16\0\0\0\0\2\0\0\0\2\0\0\0"..., 1024) = 1024
mmap(NULL, 1884160, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c1570000
lseek(3, 4096, SEEK_SET) = 4096
read(3, "\1\4\0\0\21\4\0\0!\4\0\0\331\3\364\17\2\0\4\0\0\0\0\0\0\0\0\0\363\0175\2"..., 1880064) = 1880064
open("/dev/mapper/vgtrsen-u02", O_RDONLY) = 4
uname({sys="Linux", node="trsen.test.hpay", ...}) = 0
ioctl(4, BLKGETSIZE64, 8736823312384) = 0
close(4) = 0
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=2512, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75e5000
read(4, "# Locale name alias data base.\n#"..., 4096) = 2512
read(4, "", 4096) = 0
close(4) = 0
munmap(0x7fa1c75e5000, 4096) = 0
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/e2fsprogs.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US.utf8/LC_MESSAGES/e2fsprogs.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/e2fsprogs.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/e2fsprogs.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/e2fsprogs.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/e2fsprogs.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa1c75e5000
write(1, "Filesystem at /dev/mapper/vghpcp"..., 85Filesystem at /dev/mapper/vgtrsen-u02 is mounted on /u02; on-line resizing required
) = 85
write(1, "old_desc_blocks = 459, new_desc_"..., 45old_desc_blocks = 459, new_desc_blocks = 509
) = 45
access("/sys/fs/ext4/features/meta_bg_resize", R_OK) = 0
open("/u02", O_RDONLY) = 4
ioctl(4, 0x40086610, 0x7ffd27f5eec8) = -1 EPERM (Operation not permitted)
write(2, "resize2fs", 9resize2fs) = 9
write(2, ": ", 2: ) = 2
write(2, "Permission denied to resize file"..., 38Permission denied to resize filesystem) = 38
ioctl(2, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(2, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
write(2, "\n", 1
) = 1
exit_group(1) = ?
+++ exited with 1 +++

[root@trsen /]# resize2fs /dev/mapper/vgtrsen-u02 
resize2fs 1.43-WIP (20-Jun-2013)
Filesystem at /dev/mapper/vgtrsen-u02 is mounted on /u02; on-line resizing required
old_desc_blocks = 459, new_desc_blocks = 509
resize2fs: Permission denied to resize filesystem

[root@trsen /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_hpdpre-lv_root
50G 25G 22G 54% /
tmpfs 120G 72K 120G 1% /dev/shm
/dev/sda1 477M 81M 367M 19% /boot
/dev/mapper/vg_hpdpre-lv_home
39G 30G 7.4G 80% /home
/dev/mapper/vgtrsen-u01
99G 29G 66G 31% /u01
/dev/mapper/vgtrsen-u02
7.2T 6.7T 108G 99% /u02
[root@trsen /]# umount /u02
[root@trsen /]# resize2fs /dev/mapper/vgtrsen-u02 
resize2fs 1.43-WIP (20-Jun-2013)
Please run 'e2fsck -f /dev/mapper/vgtrsen-u02' first.

[root@trsen /]# e2fsck -f /dev/mapper/vgtrsen-u02
e2fsck 1.43-WIP (20-Jun-2013)
Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/mapper/vgtrsen-u02: 3499/240414720 files (1.3% non-contiguous), 1802779091/1923298304 blocks
[root@trsen /]# 
[root@trsen /]# mount /dev/mapper/vgtrsen-u02 /u02
[root@trsen /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_hpdpre-lv_root
50G 25G 22G 54% /
tmpfs 120G 72K 120G 1% /dev/shm
/dev/sda1 477M 81M 367M 19% /boot
/dev/mapper/vg_hpdpre-lv_home
39G 30G 7.4G 80% /home
/dev/mapper/vgtrsen-u01
99G 29G 66G 31% /u01
/dev/mapper/vgtrsen-u02
7.2T 6.7T 108G 99% /u02
[root@trsen /]# cd /u02
[root@trsen u02]# ls -lat
total 40
dr-xr-xr-x. 28 root root 4096 Jan 29 16:12 ..
drwxr-xr-x 7 oracle oinstall 4096 Jan 2 15:54 .
drwxr-xr-x 3 oracle oinstall 4096 Jan 2 14:04 media
drwxr-xr-x 3 oracle oinstall 4096 Nov 22 13:16 rman
drwxr-xr-x 4 oracle oinstall 4096 Nov 19 18:40 arch
drwxr-xr-x 3 oracle oinstall 4096 Nov 19 18:40 oradata
drwxr-xr-x 2 oracle oinstall 16384 Nov 19 17:51 lost+found
[root@trsen u02]# resize2fs /dev/mapper/vgtrsen-u02 
resize2fs 1.43-WIP (20-Jun-2013)
Filesystem at /dev/mapper/vgtrsen-u02 is mounted on /u02; on-line resizing required
old_desc_blocks = 459, new_desc_blocks = 509
The filesystem on /dev/mapper/vgtrsen-u02 is now 2133013504 blocks long.

可能是因为之前对此设备做了快照时，产生一些无操作后，导致文件系统产生了不一致的状态，所以通过强制一致性检查后，再进行生效即可