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Server Filesystems |
  
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Server Filesystems |
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Introduction
The ImageServer allows configuration of multiple filesystems for storage of image data. The filesystems can be locally mounted drives, NAS devices accessed through a UNC path, or a SAN. The ImageServer allows assigning configured filesystems to a specific Tier of storage. The ImageServer will store incoming studies to the available filesystems configured for Tier 1 with preference given to the filesystem with the most free space available.
Filesystems can be added at any time to the ImageServer through the Web GUI. They cannot be removed, however, they can be disabled from the Web GUI. Filesystems can also be made "Read Only". When made "Read Only", new studies will not be added to the filesystem.
See the Disk Management section for details on disk management and the compression section for details on compressing online studies.
Filesystem Tiers
Filesystems are assigned to specific tiers of storage through the Filesystem configuration page. Typically the first tier of storage would have the fastest access speeds. Subsequent filesystem tiers would have slower access disk.
Newly arriving studies are only placed on the first storage tier. Tier1 Retention rules configure when a study is eligible to be migrated from the first tier. Note that all migration is watermark based, and studies will only be migrated when a filesystem is above the high watermark. The tier 1 retention rules specify when a study is eligible for migration, and the relative order that studies will be migrated based on the calculated migration date. There are no rules specified when a study is eligible to be migrated from subsequent tiers of storage. The studies will be migrated in the same order that they were migrated from the first tier of storage. Finally, when studies reach the lowest level tier, they are deleted or purged from that filesystem depending on how the filesystem is configured.
NAS Based Filesystems
When configuring a NAS device, the filesystem should be accessed through a UNC path (ie, a path such as \\127.0.0.1\ShareName). When a UNC path is used, a matching user account must be configured on the NAS system and on the system running the Windows Service. The Windows Service must be setup to "Logon" as this shared user account, and the user must be authorized to access the shared folder on the NAS for the filesystem. This is typically done by having the same administrator password on both the NAS and the server running the Windows service. Filesystems are configured this way (as opposed to locally mounting the drive) so that the service can always access the NAS. Mounting of filesystems is constrained to when a user is logged onto the computer, and thus does not work properly with the service.
Watermarks
As detailed in the Disk Management section, the ImageServer will periodically check a filesystem to detect when a disk management needs to be done, and in turn may migrate studies to a new tier, delete the studies, or purge the studies form the filesystem. Because there can be some lag time between when the filesystem is detected to be above the high watermark, and when the actual activity is done to reduce the disk usage, it is recommended that the high watermark settings be low enough to allow some overshooting of the high watermark by the software. The high watermark should be set low enough to allow several hours worth of data to be stored on the drive without filling up the drive. Setting the high watermark low enough will reduce the risk of potential problems with the disk filling up.