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public:8067_faq:discrepancy_between_ahsaycbs_storage_statistics_vs_physical_data_size
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FAQ: Why is there a discrepancy between AhsayCBS storage statistics vs physical data size on a storage device?
Article ID:
8067
Reviewed:
07/02/2020
Product Version:
Ahsay Software: v7.3.x to v7.17.2.x, v8.1.0.24 to 8.1.1.174, v8.3.0.30 or above
Audience
This article is for AhsayCBS Administrator’s (partners) who have inquiry about the discrepancy between AhsayCBS storage statistics vs physical data size on a storage device.
Description
Starting from v7 and continuing in v8, Ahsay implemented a new storage format for backup data on AhsayCBS and cloud destinations to enhance the backup performance and improve the overall performance of AhsayCBS backup server. All files backed up are stored in either 16 MB or 32 MB blocks depending in the file size on the backup destination(s), which can be on AhsayCBS server, local, and or cloud storage destinations.
• The backup and storage of multiple small files (< 16 MB) are combined and stored in 16 MB data blocks or “shared blocks”. Depending on the file type and size of the source file, a 16 MB data block can contain a few small files or even hundreds of small files.<li/>
• The backup and storage of large files (>32MB) are broken down and stored in 32 MB data blocks. For example: a file with size of 100 MB would be split up and stored as 4 'block' files: 3 x 32 MB and 1 x 4 MB.
Due to the new data storage format there can be discrepancies between storage statistics reported by the Operating System which is considerably larger than the storage statistics reported by AhsayCBS as:
• AhsayCBS storage statistics (on an application Level) represents the files/folders in a backup set(s), which are restorable in both the data area and retention area.
• The storage statistics reported by the Operating System which is the size on of the backup set data on the disk or cloud storage represents the physical 16 MB and 32 MB block files.
The discrepancy stems from the handling of small files stored in the 16 MB blocks or “shared blocks” in v7/v8.
• When a file has been backed up is subsequently deleted from a customer machine, on the next backup job AhsayOBM/AhsayACB will detect the change and update the related index file to mark the file as deleted and change the location of the files from the data area to retention area. To minimize disk I/O load on the AhsayCBS server, the deleted remains in the 16 MB block.
• Once the deleted file in the retention area exceeds the retention policy settings, the reference to the delete file is removed from the index file only, to minimize disk I/O load on the AhsayCBS server it is not physically removed from the 16 MB block file, therefore the AhsayCBS storage statistics will report small size.
A 16 MB block or “share block” file can only be physically deleted from the storage device, once all the files stored in the block are changed from the customer machine, moved to retention area, and exceeds the retention policy.
However, in the backup and storage of large files the physical 32 MB block files are removed from the storage device, once the deleted file in the retention area exceeds the retention policy settings.
public/8067_faq/discrepancy_between_ahsaycbs_storage_statistics_vs_physical_data_size.1581063013.txt.gz · Last modified: 2020/02/07 16:10 by yuk.cheng