FORMULA for Disk Reconstruction

Question

Is there a formula out there that I can use to figure on how long it will take to rebuild/reconstruct disk array when adding additional drives?   Thanks in advance   -Yellow Boy:smileyindifferent:

warwizard55 · Answer

ok formulas,

(Size of one drive in M/B Divided by Transfer rate (40 M/B, 80M/B, 160 M/B, or 320 M/B) , Times # drives online for reading task.

Plus

Size of one drive in M/B Divided by Transfer rate for the write task.)

This yields the minimum time (when rebuilding the arrry with the BIOS and no other I/O is being run)

If the rebuild is being done in conjunction with other I/O such as operating system overhead, and 50 users doing email... your RAID management S/W has a throttle setting that devotes a % of the transfer bandwidth to the rebuild process. Just divide the amount of time from the previous calculation by the % of the I/O devoted to the rebuild (expressed as a decimal fraction 15%=.15)

Example: PERC II (40 M/B per second transfer rate) 8 drive RAID 5 with 73 GB drives, rebuilding in the BIOS... 40 MB/s Times 3600 seconds in an hour= 144 GB/hr on a 584 GB task, or about 4 hours.

The same job with a load still on the server and only 20% dedicated to the rebuild, will take 20 hours.

In addition the write cache is disabled whenever the array is degraded, so system performance will suffer a 20% to 40% performance hit depending on the exact mix or reads and writes in your load.

warwizard

PowerEdge HDD/SCSI/RAID

FORMULA for Disk Reconstruction

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