HP StoreAll Storage - Manual (Page 155)

16 Using file allocation
This chapter describes how to configure and manage file allocation.
Overview
X9000 Software allocates new files and directories to segments according to the allocation policy
and segment preferences that are in effect for a client. An allocation policy is an algorithm that
determines the segments that are selected when clients write to a file system.
File allocation policies
Different allocation policies can be set for files and directories. The following table lists the available
allocation policies.
By default, file systems use the RANDOM allocation policy, and all segments are preferred. These
defaults are adequate for most cluster environments. In some cases, HP Support may recommend
that you change the defaults as follows to optimize file storage for your system:
•
Change the default file and directory allocation policy.
•
Prefer a pool of segments for storing all new files and directories.
•
Declare the first segment where a file or directory will be stored.
IMPORTANT: Changing the default allocation policy and segment preferences will alter file
system storage behavior. Contact HP Support before changing either of these defaults.
Although the allocation policy and segment preferences are set locally on X9000 clients, they are
set on the NFS or CIFS server for NFS or CIFS clients. X9000 clients write directly to file serving
nodes according to the file allocation settings in effect for them. In contrast, NFS and CIFS clients
write to a file system only via their NFS or CIFS server; therefore, the allocation policy and segment
preferences that are in effect on the NFS or CIFS server determine the segments where the data is
stored.
To choose a segment, an X9000 client or NFS/CIFS server evaluates the allocation policy and
segment preferences that are defined for it.
The following table lists the file allocation policies.
Description Policy
Lets the X9000 Software select the allocation policy. AUTOMATIC
Allocates files to the segment where its parent directory is located. DIRECTORY
Allocates files to a file serving node’s local segments. LOCAL
Allocates files to a randomly chosen segment among preferred segments. This is the default
policy. RANDOM
Allocates files to preferred segments in segment order, returning to the first segment (or the
designated starting segment) when a file has been allocated to the last segment. ROUNDROBIN
Allocates files to one segment until the segment’s storage limit is reached, and then moves to
the next segment as determined by the AUTOMATIC file allocation policy. STICKY
Sets the directory allocation policy only. Causes the directory allocation policy to revert to its
default, which is the policy set for file allocation. Use NONE only to set file and directory
allocation to the same policy. NONE
For clusters with more than 16 file serving nodes, takes a subset of the servers to be used for
file creation and rotates this subset on a regular periodic basis. This policy should be used
only under the direction of HP Support. HOST_ROUNDROBIN_NB
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