For 64-bit kernels on disk layout 5, the size of the filesystem at creation time determines the default file system block size. The block size, in turn, dictates the maximum size to which a filesystem can be grown.

A block size can optionally be specified using the -o b size= option when creating the filesystem via mkfs. If the block size is not specified when creating a filesystem, the block size defaults to the following values:

Filesystem size at creation      Default block size
up to 4TB                                   1k
4TB to 8TB                                 2k
8TB to16TB                                4k
greater than 16TB                      8k

If a filesystem larger than the maximum supported size for a given block size will be needed in the future, specify a larger block size than the default. There is no way to increase the block size once the filesystem is created.

For example, if a 3TB file system was created using the default 1K block size, it can only be increased to 4TB. However, if the same 3TB file system were created with a block size of 2K, it can be grown up to 8TB.

Block size Maximum      Filesystem size
1k                                     4TB
2k                                     8TB
4k                                     16TB
8k                                     32TB

To grow the filesystem past the supported size given its block size, back up the data, recreate the filesystem (using the appropriate block size) and restore the data.

For disk layout 6 and 7, the size of the filesystem at creation time still determines the default file system block size, and the block size still dictates the maximum size to which a file system can be grown. However, the maximum filesystem sizes are larger. Creating a filesystem greater than 32TB, or growing an existing file system to a size larger than 32TB, requires a Storage Foundation Enterprise license key.

Block size Maximum      Filesystem size
1k                                     32TB
2k                                     64TB
4k                                     128TB
8k                                     256TB

If your disk layout is version 5 , the disk layout version of the filesystem can be upgraded to version 6, allowing a larger filesystem size for a given block size. The disk layout can be determined -- and upgraded -- via the vxupgrade command. The upgrade is an online process that can be run while the file system is mounted.