Virtual TapeServer 8.4 Configuration Guide

210 | Virtual TapeServer Configuration Guide
Adding a vault to a GFS cluster
Note If path failover is configured in the environment, be sure to reference the multipathed mapper
device instead of the sd device in the following procedure. For example, reference
/dev/mapper/mpathX instead of /dev/sdX.
Before configuring the vault, consider the following recommendations:
l The minimum partition size is 1TB.
l The maximum partition size is 5TB, which is determined by the amount of memory required to
check a file system created on the partition. Running a file system check (fsck) requires
system memory that is above and beyond the memory used for the operating system and
kernel.
Example for EXT3 file systems:
Checking is done using bitmaps, three for blocks, and up to six for inodes. For example, for a
ext[2,3] file system that is 5TB with a block size of 4KB, divide 5TB by 4KB and then divide by
8 bits per byte to find amount of memory needed for each block bitmap:
5497558138880 / 4096 = 1342177280 blocks
1342177280 / 8 = 167772160 bytes per block bitmap
Now, take 5TB again and divide by 8K inodes per group and then divide by 8 bits per byte to
find the amount of memory needed for each inode bitmap:
5497558138880 / 8192 = 671088640 inodes
671088640 / 8 = 83886080 bytes per inode bitmap
Finally, there are three block bitmaps and up to six inode bitmaps:
(167772160 * 3) + (83886080 * 6) = 1006632960
The file system requires approximately 1GB of free memory to run fsck (the fsck.ext[2,3]
command) if there are no directories. In addition, fsck.ext[2,3] keeps a directory information
bitmap, which requires 12 bytes for each directory.
Example for GFS file systems:
Each block of memory in the file system requires approximately one byte of additional
memory. So, to estimate the amount of memory you will need to run fsck (the gfs_fsck
command) on your file system, divide the file system size (in bytes) by the block size. For
example, for a GFS file system that is 5TB with a block size of 4KB, divide 5TB by 4KB:
5497558138880 / 4096 = 1342177280