User manual REDHAT LVM ADMINISTRATOR 5.0 CONFIGURATION

[. . . ] LVM Administrator's Guide Configuration and Administration 5. 0 ISBN: N/A Publication date: LVM Administrator's Guide This book describes the LVM logical volume manager, including information on running LVM in a clustered environment. The content of this document is specific to the LVM2 release. LVM Administrator's Guide: Configuration and Administration Copyright © You need to override the YEAR enity in your local ent file Red Hat, Inc. Copyright © You need to override the YEAR enity in your local ent file Red Hat Inc. . This material may only be distributed subject to the terms and conditions set forth in the Open Publication License, V1. 0 or later with the restrictions noted below (the latest version of the OPL is presently available at http://www. opencontent. org/openpub/). Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. [. . . ] The number of stripes cannot be greater than the number of physical volumes in the volume group (unless the --alloc anywhere argument is used). The stripe size should be tuned to a power of 2 between 4kB and 512kB, and matched to the application's I/O that is using the striped volume. The -I argument of the lvcreate command specifies the stripe size in kilobytes. If the underlying physical devices that make up a striped logical volume are different sizes, the maximum size of the striped volume is determined by the smallest underlying device. For example, in a two-legged stripe, the maximum size is twice the size of the smaller device. In a three-legged stripe, the maximum size is three times the size of the smallest device. The following command creates a striped logical volume across 2 physical volumes with a stride of 64kB. The logical volume is 50 gigabytes in size, is named gfslv, and is carved out of volume group vg0. lvcreate -L 50G -i2 -I64 -n gfslv vg0 As with linear volumes, you can specify the extents of the physical volume that you are using for the stripe. The following command creates a striped volume 100 extents in size that stripes 35 Chapter 4. LVM Administration with CLI Commands across two physical volumes, is named stripelv and is in volume group testvg. The stripe will use sectors 0-50 of /dev/sda1 and sectors 50-100 of /dev/sdb1. # lvcreate -l 100 -i2 -nstripelv testvg /dev/sda1:0-50 /dev/sdb1:50-100 Using default stripesize 64. 00 KB Logical volume "stripelv" created 4. 1. 3. Creating Mirrored Volumes When you create a mirrored volume, you specify the number of copies of the data to make with the -m argument of the lvcreate command. Specifying -m1 creates one mirror, which yields two copies of the file system: a linear logical volume plus one copy. Similarly, specifying -m2 creates two mirrors, yielding three copies of the file system. The following command creates a mirrored logical volume with a single mirror. The volume is 50 gigabytes in size, is named mirrorlv, and is carved out of volume group vg0: lvcreate -L 50G -m1 -n gfslv vg0 An LVM mirror divides the device being copied into regions that, by default, are 512KB in size. You can use the -R argument to specify the region size in MB. LVM maintains a small log which it uses to keep track of which regions are in sync with the mirror or mirrors. By default, this log is kept on disk, which keeps it persistent across reboots. You can specify instead that this log be kept in memory with the --corelog argument; this eliminates the need for an extra log device, but it requires that the entire mirror be resynchronized at every reboot. The following command creates a mirrored logical volume from the volume group bigvg. The logical is named ondiskmirvol and has a single mirror. [. . . ] Run lvchange -ay vg1/lvol2. This solution involves storing hostnames inside the volume group metadata. 92 Appendix D. LVM Volume Group Metadata The configuration details of a volume group are referred to as the metadata. By default, an identical copy of the metadata is maintained in every metadata area in every physical volume within the volume group. LVM volume group metadata is small and stored as ASCII. [. . . ]