HP StorageWorks Storage Mirroring for Linux User's Guide (T2558-96317, June 2009)

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Replication capabilities
Storage Mirroring replicates all file and directory data in the supported Linux file systems. (See
System requirements on page 2-1 for the file systems supported). It does not replicate items that
are not stored on the file system, such as pseudo-file systems like /proc and /sys. In addition, note
the following.
 Data that will be replicated must reside on a Storage Mirroring partition, which is specially
mounted with the Storage Mirroring file system (DTFS) driver. DTFS is a virtual file system that
monitors the storage file system so that data changes can be captured. DTFS is a transparent file
system. Existing mount points may be available for replication, but the data on those mount point
can only be replicated if they are DTFS mount points. The DTSetup utility allows you to specify
which mount points should be DTFS mount points. See Configuring your servers using
DTSetup on page 2-4 for more information on the DTSetup utility.
 DTFS mount points are identified in the Management Console by dtfs in the mount point name.
 Storage Mirroring is compatible with NFS and Samba services as long as they are mounted on top
of Storage Mirroring. Storage Mirroring should be mounted just above the storage file system.
Additionally, NFS and Samba should be started after the Storage Mirroring daemon.
 Do not select the root as a replication mount point.
 If you have a single drive system, mount DTFS to any of the subdirectories directly under root
that you want to replicate.
 If you select data stored on a recursive mount point for replication, a mirror will never finish.
Storage Mirroring does not check for data stored on recursive mount points.
 If any directory or file contained in your replication set specifically denies permission to the
account running the Storage Mirroring daemon, the attributes of the file on the target will not be
updated because of the lack of access.
 If you are using soft links, keep in mind the following.
 If a soft link to a directory is part of a replication set rule’s path above the entry point to the
replication set data, that link will be created on the target as a regular directory if it must be
created as part of the target path.
 If a soft link exists in a replication set (or is moved into a replication set) and points to a file
or directory inside the replication set, Storage Mirroring will remap the path contained in that
link based on the Storage Mirroring target path when the option RemapLink is set to the
default value (1). If RemapLink is set to zero (0), the path contained in the link will retain its
original mapping.
 If a soft link exists in a replication set (or is moved into a replication set) and points to a file
or directory outside the replication set, the path contained in that link will retain its original
mapping and is not affected by the RemapLink option.
 If a soft link is moved out of or deleted from a replication set on the source, that link will be
deleted from the target.
 If a soft link to a file is copied into a replication set on the source and the operating system
copies the file that the link pointed to rather than the link itself, then Storage Mirroring
replicates the file copied by the operating system to the target. If the operating system does
not follow the link, only the link is copied.
 If a soft link to a directory is copied into a replication set on the source and the operating
system copies the directory and all of its contents that the link pointed to rather than the link
itself, then Storage Mirroring replicates the directory and its contents copied by the operating
system to the target. If the operating system does not follow the link, only the link is copied.
 If any operating system commands, such as chmod or chown, is directed at a soft link on the
source and the operating system redirects the action to the file or directory which the link
references, then if the file or directory referenced by the link is in a replication set, the
operation will be replicated for that file to the target.
 The operating system redirects all writes to soft links to the file referenced by the link.
Therefore, if the file referenced by the symbolic link is in a replication set, the write operation
will be replicated to the target.