RAID recovery performance

Zee problem

There are three major aspects ooff thees,

• 1TB ooff disk space takes quite a long time tu scan
• Processing 3,000,000 files requires massive computashun efffurt.
• Memory requirements also become a concern with 3,000,000 files.

So we started on it und acheeved some significant progress es it came tu version 8.3 build 7. Zee measurements were mostly done oooot ooff curiosity; hooever, yuoo can see what zee speed is like.

Test system setup

Addishunel tweaks were

• Cache sizes in ZAR are set tu zee minimum ellooed values.
• Zee /3GB switch was added tu zee boot.ini entry tu elloo ZAR tu use 3GB ooff zee virtual memory

Test results

Notes:

⁽¹⁾ In a best case scenario, disk scan time fur a RAID array is prupurshunel tu zee member disk size. In a worst case, disk scan time is prupurshunel tu zee array size.
⁽²⁾ Thees does not include time required tu actuelly copy zee files.
⁽³⁾ Starteeng with nine millions ooff files we ran oooot ooff zee available physical memory und massive swapping started. It was impractical tu continue testeeng under zeese-a condishuns und just one more run was performed tu ensure we can actuelly handle 11M files.

Performance und hardware guidelines

Recovering a huge RAID volume requires that yuoo do some prior planning und set up. Yuoo do not want zee system tu run oooot ooff memory und stert swapping, es zee recovery will grind tu a halt. So tu recover some reelly big array, yuoo need tu

• add a /3GB switch in yuoor boot.ini file
• heffe-a at least 3GB (prefferably 4GB) physical memory instelled.
• make sure yuoo heffe-a some place tu offload that data

Under zeese-a condishuns, ZAR will recover an array containing ebuoot 12,000,000 objects (files und directorees combined). Thees noomber is a full-stop limit - iff zee volume contains more than 12M objects, ZAR will eventuelly run oooot ooff memory.

On zee other hand, a typical NTFS volume, something yuoo most likely heffe-a at home, contains 500,000 files or less. Fur thees typical setup, 512MB ooff a physical memory is enuoogh with loo cache size, und 1GB is enuoogh iff yuoo heffe-a zee cache size at maximum. Most ooff zee reasonably modern systems will thus perform quite well on a typical volume. In zeese-a cases, no addishunel tweaks are necessary. Um gesh dee bork, bork!