在 linux 中 iostat -d 查看磁盤狀態時,有的會有如下dm-0,dm-1的設備.
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 0.19 0.57 2.92 341228 1753052
dm-0 0.27 0.56 2.88 334673 1729848
dm-1 0.00 0.00 0.00 876 0
如果有使用 LVM 則一般會生成dm-N 邏輯卷 (LogiｃVolume). 它類似於普通分區時的一個分區如 sda0 之類的.只不過它利用了 Mapper Device 機制,在 PysicalVolume 上模擬出來的設備.
查找dm-N對應的設備
１.sar -d 1
02:53:06 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz awai svctm %util
02:53:07 PM dev8-0 8.00 0.00 72.00 9.00 0.06 7.00 7.00 5.60
02:53:07 PM dev252-0 9.00 0.00 72.00 8.00 0.06 6.22 6.22 5.60
02:53:07 PM dev252-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
顯示dev252-0,dev252-1,即主設備號为dev252(sda設備號为dev8,這是linux为設備生成的內部設備號),次設備號为0,1
2.cd /dev/mapper; ll
lrwxrwxrwx 1 root root 7 Apr 3 16:12 yinbeiweb1-root -> ../dm-0
lrwxrwxrwx 1 root root 7 Apr 3 16:12 yinbeiweb1-swap_1 -> ../dm-1
可看到軟鏈到 /dev/dm-N上.
３.ll /dev/dm-*
brw-rw---- 1 root disk 252, 0 Apr 3 16:12 ../dm-0
brw-rw---- 1 root disk 252, 1 Apr 3 16:12 ../dm-1
可看到兩者的主設備號都是２５２
# sudo lvdisplay|awk '/LV Name/{n=$3} /Block device/{d=$3; sub(".*:","dm-",d); print d,n;}'
dm-0 /dev/SysVolGroup/LogVolRoot
dm-1 /dev/SysVolGroup/xen
dm-2 /dev/SysVolGroup/db1-2
dm-3 /dev/SysVolGroup/db1-2swap
dm-4 /dev/SysVolGroup/python1
dm-5 /dev/SysVolGroup/python1swap
dm-6 /dev/SysVolGroup/db1-2snap
hdX — ATA hard disk, pre-libata. You'll only see this with old distros (probably based on Linux 2.4.x or older)
sdX — "SCSI" hard disk. Also includes SATA and SAS. And IDE disks using libata (on any recent distro).
hdXY, sdXY — Partition on the hard disk hdX or sdX.
loopX — Loopback device, used for mounting disk images, etc.
loopXpY — Partitions on the loopback device loopX; used when mounting an image of a complete hard drive, etc.
scdX, srX — "SCSI" CD, using same weird definition of "SCSI". Also includes DVD, Blu-ray, etc.
mdX — Linux MDraid
dm-X — Device Mapper. Use -N to see what these are, or ls -l /dev/mapper. Device Mapper underlies LVM2 and dm-crypt. If you're using either LVM or encrypted volumes, you'll see dm-X devices.
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