HP D2D D2D Best Practices for VTL, NAS and Replication implementations (EH985- - Page 34
Disk space pre-allocation, Block / transfer size, Concurrent operations - disk full
View all HP D2D manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 34 highlights
Backup job time, assuming no housekeeping or replication windows are set Disk space pre-allocation Some backup applications allow the user to choose whether to ―pre-allocate‖ the disk space for each file at creation time, i.e. as soon as a backup file is created an empty file is created of the maximum size that the backup file can reach. This is done to ensure that there is enough disk space available to write the entire backup file. This setting has no value for D2D devices because it will not result in any physical disk space actually being allocated due to the deduplication system. It is advised that this setting is NOT used because it can result in unrealistically high deduplication ratios being presented when pre-allocated files are not completely filled with backup data or, in extreme cases, it will cause a backup failure due to a timeout if the application tries to write a small amount of data at the end of a large empty file. This results in the entire file having to be padded-out with zeros at creation time, which is a very time consuming operation. Block / transfer size Some backup applications provide a setting for block or transfer size for backup data in the same way as for tape type devices. Larger block sizes are beneficial in the same way for NAS devices as they are for virtual tape devices because they allow for more efficient use of the network interface by reducing the amount of metadata required for each data transfer. In general, set block or transfer size to the largest value allowed by the backup application. Concurrent operations For best D2D performance it is important to either perform multiple concurrent backup jobs or use multiple streams for each backup (whilst staying within the limit of concurrently open files per NAS share). Backup applications provide an option to set the maximum number of concurrent backup streams per file device; this parameter is generally referred to as the number of writers. Setting this to the maximum values shown in the table 34