IBM XIV Storage System Copy Services and Migration

Writing zeros to recover spaceOne way to recover space before you start a migration is to use a utility to write zeros acrossall free space. In a UNIX environment you could use a simple script like the one shown inExample 7-7 to write large empty files across your file system. You may need to run thesecommands many times to use all the empty space.Example 7-7 Writing zeros across your file system# The next command will write a 1 GB mytestfile.outdd if=/dev/zero of=mytestfile.out bs=1000 count=1000000# The next command will free the file allocation spacerm mytestfile.outIn a Windows environment you can use a Microsoft tool known as sdelete to write zerosacross deleted files. You can find this tool in the sysinternals section of Microsoft Technet.Here is the current URL:http://technet.microsoft.com/en-us/sysinternals/bb897443.aspxIf you instead choose to write zeros to recover space after the migration, you must initiallygenerate large amounts of empty files, which may initially appear to be counter-productive. Ittakes several days for the used space value to decrease after the script or application is run.This is because recovery of empty space runs as a background task.7.8 Resizing the XIV volume after migrationBecause of the way that XIV distributes data, the XIV allocates space in 17 GB portions(which are exactly 17,179,869,184 bytes or 16 GiB). When creating volumes using the XIVGUI this aspect of the XIV design becomes readily apparent when you enter a volume sizeand it gets rounded up to the next 17 GB cutoff.Chapter 7. Data migration 213