Sunday, December 4, 2016
How long does it take to detect array parameters
How long does it take to detect array parameters
RAID recovery time
RAID recovery time depends on both the time required to read a sample of data from a disk set and the time for analyzing the data sample and determining the array configuration parameters. However, read and analysis speeds depend on many other aspects and the resulted RAID recovery time will be limited by the worst of the components.
Statistical analysis time
The RAID recovery time depends directly on the data being analyzed. Based on some data the confident decision can be obtained immediately, while the other data can be absolutely useless for determining the parameters.
On top of that, it is practically beneficial to scan the disk not in a continuous pattern. Instead, the samples are picked randomly from a disk set.
These two factors together lead to the fact that the RAID recovery time can be different each time you run ReclaiMe Free RAID Recovery. In a successful scenario, the RAID can be recovered in minutes, in the worst case it will take several hours to complete recovery.
Disk throughput
RAID recovery involves reading a lot of data. In worst case, the entire disk set is to be read three times - for the RAID analysis, then for the filesystem analysis, and then when the files are copied out. The hardware setup affects the read speed significantly. Reconfiguring the storage subsystem can sometimes reduce recovery time by the factor of ten.
The following considerations apply:
- If you connect the disk to a SATA port on motherboard, you get 30 to 50 MB/sec throughput. A modern hard drive can deliver data faster, but realistic processing speed does not exceed 50 MB/sec with a rotational hard drive. The throughput is defined per SATA port, meaning that if you have two drives connected to SATA ports, data is processed twice as fast as long as CPU can handle it.
- If you use USB, make sure everything works in at least USB 2.0 mode. USB 1.1 is unacceptably slow for data recovery use; however, the USB 1.1 hubs are still produced. USB 3.0 devices are not very stable as of spring 2012. You should probably avoid USB 3.0 hubs till at least 2013. Anyway, if something goes wrong with an USB 3.0 device, it falls back to USB 2.0 mode, so you dont lose much.
- USB 2.0 provides about 15 MB/sec throughput per root port. If you connect several hard drives to an USB hub, their combined throughput is limited to 15 MB/sec.
- If you use multiple disk image files during RAID recovery, you should evenly distribute these image files across as many physical hard drives as possible. There is a singificant penalty associated with mechanical disk seeks if you put multiple images onto one hard drive.
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