Management Software

3 Responses to 'Can you please give me some names of Volume Management Software?'

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1. SeasonedToker said,
   
   

   on August 31st, 2010 at 6:08 pm

   Paragon Hard Drive manager is a miracle worker I won’t even recommend any other programs it should cover all tools you need in one and do its job well.

2. Jake said,
   
   

   on August 31st, 2010 at 6:46 pm

   partition magic

3. cy637_50n1c said,
   
   

   on August 31st, 2010 at 7:38 pm

   Volume management is not new in the -ix world (UNIX®, AIX, and so forth). And logical volume management (LVM) has been around since Linux® kernel 2.4v1 and 2.6.9v2. This article reveals the most useful features of LVM2—a relatively new userspace toolset that provides logical volume management facilities—and suggests several ways to simplify your system administration tasks. Based on reader feedback, the author has updated Listings 10, 14, 15, and 16. -Ed.

   Logical volume management (LVM) is a way systems can abstract physical volume management into a higher-level and usually simpler paradigm. By using LVM, all physical disks and partitions, no matter what size and how scattered they are, can be abstracted and viewed as a single storage source. For example, in the layout of physical-to-logical mapping shown in Figure 1, how could the user create a filesystem of, say 150GB, since the biggest disk is 80GB large?

   Figure 1. Physical-to-logical mapping
   Physical-to-logical mapping

   By aggregating partitions and whole disks into a virtual disk, LVM can sum small storage spaces into a bigger, consolidated one. This virtual disk, in LVM terms, is called volume group.

   And the possibility of having a filesystem bigger than your biggest disk isn’t the only magic feature of this high-level paradigm of storage management. With LVM, you can also:

   * Add disks/partitions to your disk-pool and extend existing filesystems online
   * Replace two 80GB disks with one 160GB disk without the need to bring the system offline or manually move data between disks
   * Shrink filesystems and remove disks from the pool when their storage space is no longer necessary
   * Perform consistent backups using snapshots (more on this later in the article)

   LVM2 refers to a new userspace toolset that provides logical volume management facilities In Linux. It is fully backwards-compatible with the original LVM toolset. In this article, you’ll see the most useful features of LVM2 as well as some other possible uses to simplify your system administration tasks. (By the way, if you’re looking for a more basic guide to LVM, try the LVM HowTo listed in the Resources section below).

   Let’s look at how the LVM is organized.

   LVM organization

   The LVM is structured in three elements:

   * Volumes: physical and logical volumes and volume groups
   * Extents: physical and logical extents
   * Device mapper: the Linux kernel module

   Volumes

   Linux LVM is organized into physical volumes (PVs), volume groups (VGs), and logical volumes (LVs). Physical volumes are physical disks or physical disk partitions (as in /dev/hda or /dev/hdb1). A volume group is an aggregation of physical volumes. And a volume group can be logically partitioned into logical volumes.

   Figure 2 shows a three-disk layout.

   Figure 2. Physical-to-logical volume mapping
   Physical to logical volume mapping

   All four partitions in physical disk 0 (/dev/hda[1-4]), as well as the whole of physical disk 1 (/dev/hdb) and physical disk 2 (/dev/hdd), were added as PVs to volume group VG0.

   The volume group is where the magic of n-to-m mapping is done (as in, n PVs can be seen as m LVs). So after the assignment of PVs to the volume group, you can create a logical volume of any size (to the maximum of the VG size). In the example in Figure 2, a volume group named LV0 was created, leaving some free-space for other LVs (or for posterior LV0 growth).

   Logical volumes are the LVM equivalent of physical disks partitions—for all practical purposes, they are physical disk partitions.

   So, after the creation of an LV, you can use it with whatever filesystem you prefer and mount it under some mount point to start using it. Figure 3 shows a formatted logical volume, LV0, mounted under /var.

   Figure 3. Physical volumes to filesystem mapping
   Physical volumes to filesystem mapping

   Extents

   In order to do the n-to-m, physical-to-logical volumes mapping, PVs and VGs must share a common quantum size for their basic blocks; these are called physical extents (PEs) and logical extents (LEs). Despite the n-physical to m-logical volume mapping, PEs and LEs always map 1-to-1.

   With LVM2, there’s no limit on the maximum numbers of extents per PV/LV. The default extent size is 4MB, and there’s no need to change this for most configurations, because there is no I/O performance penalty for smaller/bigger extent size. LVM tools usage, however, can suffer from high extent count, so using bigger extents can keep the extent count low. Be aware, however, that different extent sizes can’t be mixed in a single VG, and changing the extent size is the single unsafe operation with the LVM: It can destroy data. The best advice is to stick with the extent size chosen in the initial setup.

   Different extent sizes means different VG granularity. For instance, if you choose an extent size of 4GB, you can only shrink/extend LVs in steps of 4GB.

   Figure 4 shows the same layout used in previous examples with the PEs and LEs shown (the free space inside VG0 is also formed of free LEs, even though they’re not shown).

   Figure 4. Physical to logical extent mapping
   Physical to logical extent mapping

   Also note the extent allocation policy in Figure 4. LVM2 doesn’t always allocate PEs contiguously; for more details, see the Linux man page on lvm (see the Resources below for a link). The system administrator can set different allocation policies, but that isn’t normally necessary, since the default one (called the normal allocation policy) uses common-sense rules such as not placing parallel stripes on the same physical volume.

   If you decide to create a second LV (LV1), the final PE distribution may look like the one shown in Figure 5.

   Figure 5. Physical to logical extent mapping
   Physical to logical extent mapping

   Device mapper

   Device mapper (also known as dm_mod) is a Linux kernel module (it can be built-in too), upstream since kernel 2.6.9. Its job (as the name says) is to map devices—it is required by LVM2.

   In most major distributions, Device mapper comes installed by default, and it is usually loaded automatically at boot time or when LVM2/EVMS packages are installed or enabled (EVMS is an alternative tool; more on that in Resources). If not, try to modprobe for dm_mod and then check your distro’s documentation for how to enable it at boot time: modprobe dm_mod.

   When creating VGs and LVs, you can give them a meaningful name (as opposed to the previous examples where, for didactic purposes, the names VG0, LV0, and LV1 were used). It is the Device mapper’s job to map these names correctly to the physical devices. Using the previous examples, the Device mapper would create the following device nodes in the /dev filesystem:

   * /dev/mapper/VG0-LV0
   o /dev/VG0/LV0 is a link to the above
   * /dev/mapper/VG0-LV1
   o /dev/VG0/LV1 is a link to the above

   (Notice the name format standard: /dev/{vg_name}/{lv_name} -> /dev/mapper/{vg_name}{lv_name}).

   As opposed to a physical disk, there’s no raw access to a volume group (meaning there’s no such thing as a /dev/mapper/VG0 file or you can’t dd if=/dev/VG0 of=dev/VG1). You usually deal with these using the lvm(8) command(s).

   Common tasks

   Some common tasks you’ll perform with LVM2 are systems verification (is LVM2 installed?) and volume creation, extension, and management.

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