Logical Volume Management (LVM) is a powerful tool for managing disk storage in Linux and other Unix-like systems. It allows for flexible allocation and resizing of storage without the limitations imposed by traditional partitioning schemes. A key command within the LVM toolkit is `lvresize`, which provides the means to change the size of a logical volume (LV). This article will delve into the intricacies of `lvresize`, exploring its functionality, comparing it to related commands, and providing practical examples to illustrate its usage in various scenarios. We'll also address common questions and misconceptions, such as "lvresize 100% free" and the implications of shrinking logical volumes.
Understanding `lvresize`
The `lvresize` command modifies the size of an existing logical volume. The size is specified in logical extents (LEs), which are the fundamental units of storage within an LVM volume group. The crucial aspect of `lvresize` is its ability to handle both expansion and reduction of logical volumes. The flexibility of the command lies in the way size changes are specified:
* Adding or Subtracting Extents: Using the `+` or `-` sign before the numerical value adds to or subtracts from the current size of the logical volume. For example, `lvresize -L +10G /dev/mapper/vg0-lv0` would increase the size of the logical volume `/dev/mapper/vg0-lv0` by 10 gigabytes (assuming each LE is 4MB).
* Setting an Absolute Size: Without the `+` or `-` sign, the specified value represents the *new* absolute size of the logical volume. For instance, `lvresize -L 20G /dev/mapper/vg0-lv0` would set the size of `/dev/mapper/vg0-lv0` to exactly 20 gigabytes, regardless of its current size. This can lead to shrinking the LV if the new size is smaller than the existing one.
`lvresize` vs `lvextend`
While both `lvresize` and `lvextend` are used to increase the size of logical volumes, there's a subtle but significant difference. `lvextend` *only* extends the size of a logical volume. It cannot shrink a logical volume. `lvresize`, on the other hand, can both extend and reduce the size of a logical volume. Therefore, `lvresize` is the more versatile command, capable of handling a wider range of size adjustments. `lvextend` is essentially a specialized subset of `lvresize`'s functionality. In most cases, `lvresize` is preferred for its broader applicability.
`lvreduce` vs `lvresize`
`lvreduce` is a command specifically designed to shrink a logical volume. While `lvresize` can also shrink a logical volume, `lvreduce` often provides more control and safety features, particularly when dealing with filesystems that need to be shrunk in place. The key difference lies in how the commands handle the filesystem residing on the logical volume. `lvreduce` is typically more cautious, ensuring data integrity during the shrinking process, especially if the filesystem is mounted. `lvresize` can perform the same shrinking operation, but requires more manual intervention and carries a higher risk of data loss if not handled correctly. Therefore, while `lvresize` can shrink, `lvreduce` is recommended for controlled shrinking operations.
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