IBM Tivoli Storage Manager for UNIX and Linux: Backup-Archive ...

Attention: If you do not back up and restore all files that are hard-linked at thesame time, problems will occur. To ensure that hard-linked files remainsynchronized, back up all hard links at the same time and restore those same filestogether.||||||||||Understanding how sparse files are handledSparse files do not have disk space allocated for every block in the whole addressspace, leading to holes within the file. Holes are detected by their content, which isalways zeros, and these zeros take up space. The default is to restore the sparse filewithout the holes, which would leave more free disk space. The Tivoli StorageManager client detects sparse files during a backup operation and marks them assparse on the Tivoli Storage Manager server. See “Makesparsefile” on page 285 formore information.Tivoli Storage Manager backs up a sparse file as a regular file if client compressionis off. See “Compression” on page 211 for more information.Understanding how NFS hard and soft mounts are handledWhen Tivoli Storage Manager connects a backup-archive client to an NFS filesystem, you can use either a hard mount or a soft mount. Tivoli Storage Manageruses the nfstimeout option setting to determine how long to wait for an NFSsystem call to respond before timing out; this applies to hard and soft mounts. Thedefault is 0 seconds. This means that Tivoli Storage Manager uses the defaultbehavior of NFS system calls.You should be aware of the consequences of hard and soft mounts if the mountbecomes stale (for example, if the server for the file system is not available).HardSoftmount— If the NFS file system is hard mounted, the NFS daemons will tryrepeatedly to contact the server. The NFS daemon retries will not time out,will affect system performance, and you cannot interrupt them, but controlwill return to Tivoli Storage Manager when the nfstimeout value isreached.mount— If the NFS file system is soft mounted, NFS will try repeatedly tocontact the server until either:v A connection is establishedv The NFS retry threshold is metv The nfstimeout value is reachedWhen one of these events occurs, control returns to the calling program.Note: On Solaris and HP-UX, the nfstimeout option can fail if the NFSmount is hard. If a hang occurs, deactivate the nfstimeout optionand mount the NFS file system soft mounted, as follows:mount -o soft,timeo=5,retry=5 machine:/filesystem /mountpointThe parameters are defined as follows:soft Generates a soft mount of the NFS file system. If an erroroccurs, the stat() function returns with an error. If the optionhard is used, stat() does not return until the file system isavailable.118 IBM Tivoli Storage Manager for UNIX and Linux: Backup-Archive Clients Installation and User’s Guide