Iostat A Partition

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Hey guys,

I need to use iostat to diagnose a disk latency problem we think we may be having.

So if I have this disk partition:

[root@uszmpdblp010la mysql]# df -h /mysql Filesystem Size Used Avail Use% Mounted on
/dev/mapper/MysqlVG-MysqlVol
9.9G 1.1G 8.4G 11% /mysql

And I want to correlate that to the output of fdisk -l, so that I can feed the disk partition I want to iostat, how would I go about that?

Here is my output from fdisk -l

[root@uszmpdblp010la mysql]# fdisk -l

Disk /dev/cciss/c0d0: 146.7 GB, 146778685440 bytes
255 heads, 32 sectors/track, 35132 cylinders Units = cylinders of 8160 * 512 = 4177920 bytes

Device Boot Start End Blocks Id System
/dev/cciss/c0d0p1 * 1 120 488281 83 Linux Partition 1 does not end on cylinder boundary.
/dev/cciss/c0d0p2 121 35131 142841947+ 8e Linux LVM
Partition 2 does not end on cylinder boundary.

Disk /dev/cciss/c0d1: 1199.8 GB, 1199865640960 bytes
255 heads, 32 sectors/track, 287192 cylinders Units = cylinders of 8160 * 512 = 4177920 bytes

Device Boot Start End Blocks Id System
/dev/cciss/c0d1p1 1 287192 1171743344 8e Linux LVM

Disk /dev/dm-0: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-0 doesn’t contain a valid partition table

Disk /dev/dm-1: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-1 doesn’t contain a valid partition table

Disk /dev/dm-2: 4294 MB, 4294967296 bytes
255 heads, 63 sectors/track, 522 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-2 doesn’t contain a valid partition table

Disk /dev/dm-3: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-3 doesn’t contain a valid partition table

Disk /dev/dm-4: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-4 doesn’t contain a valid partition table

Disk /dev/dm-5: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-5 doesn’t contain a valid partition table

Disk /dev/dm-6: 17.1 GB, 17179869184 bytes
255 heads, 63 sectors/track, 2088 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes

Disk /dev/dm-6 doesn’t contain a valid partition table

Thanks, Tim

3 thoughts on - Iostat A Partition

  • thats not a partition thats a file system on a logical volume…

    # df -h /mirror Filesystem Size Used Avail Use% Mounted on
    /dev/mapper/vg_sg1data-lvmirror
    1.0T 736G 289G 72% /mirror

    # pvs
    PV VG Fmt Attr PSize PFree
    /dev/sdb2 vg_sg1 lvm2 a– 2.00t 0
    /dev/sdc1 vg_sg1data lvm2 a– 16.37t 415.80g
    /dev/sdd1 vg_sg1data lvm2 a– 16.37t 7.87t

    or, a gnarlier case…

    # df -h /home2
    Filesystem Size Used Avail Use% Mounted on
    /dev/mapper/vgdata-lvhome2
    1.8T 306G 1.6T 17% /home2

    # pvs
    PV VG Fmt Attr PSize PFree
    /dev/md127 vgdata lvm2 a– 1.82t 19.68g

    # mdadm -D /dev/md127
    /dev/md127:
    Version : 1.2
    Creation Time : Sat Jun 14 13:18:25 2014
    Raid Level : raid1
    Array Size : 1953383232 (1862.89 GiB 2000.26 GB)
    Used Dev Size : 1953383232 (1862.89 GiB 2000.26 GB)
    Raid Devices : 2
    Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Thu Feb 19 18:40:15 2015
    State : clean
    Active Devices : 2
    Working Devices : 2
    Failed Devices : 0
    Spare Devices : 0

    Name : new.freescruz.com:0 (local to host new.freescruz.com)
    UUID : d9c90fda:9a0e5d4f:d27cf1f6:19d0b43a
    Events : 1485

    Number Major Minor RaidDevice State
    0 8 17 0 active sync /dev/sdb1
    1 8 33 1 active sync /dev/sdc1

  • lvdisplay –maps /dev/mapper/MysqlVG-MysqlVol

    That’ll show you which PVs are used for the LV. But, just given your fdisk output, I’d guess that you’re going to find that all of the extents are on /dev/cciss/c0d1p1, and watching that will produce exactly the same output as watching /dev/mapper/MysqlVG-MysqlVol.

    Try it:

    iostat -x 2 /dev/mapper/MysqlVG-MysqlVol /dev/cciss/c0d1p1

    Or just watch all of your block devices by not naming any:

    iostat -x 2

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