Hard Drive Related Cheatsheet for Linux

 

TERMINOLOGY:

  • Partition - a portion of physical hard disk space. A hard disk may contain one or more partitions. Partitions are defined by BIOS and described by partition tables stored on a harddrive.
  • Volume - a logical concept which hides the physical organization of storage space. A compatibility volume directly corresponds to a partition while LVM volume may span more than one partition on one or more physical disks. A volume is seen by users as a single drive letter.
  • Physical Volume (PV) Synonym for “hard disk”. A single physical hard drive.
  • Volume Group (VG) A set of one or more PVs which form a single storage pool. You can define multiple VGs on each system.
  • Logical Volume (LV) A usable unit of disk space within VG. LVs are used analogously to partitions on PCs or slices under Solaris: they usually contain filesystems or paging spaces (“swap”)Unlike physical partition can span multiple physical volumes that constitute VG. .
  • Root partition. Physical or logical partition what holds root filesystem and mount points for all other partitions. Can be physical partition or logical volume.

LVM Commands

  • pvcreate /dev/hda3 – creates physical volumes
  • vgcreate vg01 /dev/hda3 – creates a volume group (in this case, vg01) using the physical volume
  • lvcreate -l25000 -nlv01 vg01 – creates a logical volume using the volume group, allocating 25000 blocks
  • lvcreate -L4G -nlvroot vgraid1
  • vgextend – adds a volume to the volume group (if you add a new disk)
  • lvdisplay -v /dev/vg01/lv01
  • vgdisplay -v vg01
  • lvremove
  • vgreduce
  • mkfs -t ext3 /dev/vg01/lv02 makes a file system
  • mount /dev/vg01/lv02 /home/new mount the file system
  • mount -a mounts everything in /etc/fstab
  • vgscan –mknodes
  • vgchange -a y /dev/vgraid1 (bring /dev/vgraid1 online if it didn’t come up automatically)
  • lvscan
  • mkfs -t ext4 -t small /dev/vgraid5extra
  • umount /home/new (unmount a filesystem)
  • pvresize – update size of pv
  • lvextend -L+ /dev/vgraid0/lvsharedfiles0 
  • e2fsck -f /dev/vgraid1/lvsharedfilestemp (check filesystem)
  • resize2fs /dev/vgraid1/lvsharedfilestemp (resize the filesystem) (now works online)

MDADM stuff
RAID
raidtools2
mdadm (probably a better choice)
/etc/raid/raidtab
http://unthought.net/Software-RAID.HOWTO/
http://xtronics.com/reference/SATA-RAID-debian-for-2.6.html
http://juerd.nl/site.plp/debianraid

mdadm -Cv /dev/md0 -l1 -n2 missing /dev/sda1 –auto creates a degraded raid 1 array
mdadm -Cv -c 256 /dev/md20 -l5 -n2 missing /dev/sdf1 array with chunk size

mdadm -A -a /dev/md0 /dev/sda1

mdadm -A -a /dev/md1 /dev/sda2
fixing a degraded array
mdadm –add /dev/md7 /dev/sdd2

mkfs -t ext3 /dev/md20 – make a file system
mkfs -t ext3 -T largefile4 -E stride=16,stripe-width=2 /dev/md20 – reduce inodes, runs faster on big files

largefile4 is defined in /etc/mke2fs.conf, blocksize defaults to 4096, so with chunk size of 256, we need stride of 16

mdadm –detail –scan >> /etc/mdadm/mdadm.conf

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