Write holes raid 5

[VinnyBagOfDonuts]

Here is what I understand about write holes, correct me if i am wrong please, I want to know the risk of setting up raid 5. Write holes are caused when you are reading to or writing from a raid 5 drive while the computer unexpectedly crashes (bsod or power outage) this creates corrupted data in your parity drive. You will not realize it until you try to switch out a dead drive. If your computer unexpectedly crashes while reading or writing you could fix the write hole by recopying the files over the old so they are complete. Is this correct?

 

[Ubrales]

It is better to delete the corrupted file and then copy the in-tact file to the location you want it in.

If the corrupted file is truncated, copying over it will increase fragmentation in HDDs (not a problem with SSDs).

 

[mavroxur]

A cheap battery back-up will prevent this. And being you can pick up an APC 500VA for like $49, there's really no reason NOT to run one these days. That, or run a RAID controller with an onboard cache battery.

 

[VinnyBagOfDonuts]

So I am correct about it only happening if a sudden shutdown occurs while writing to the disc?

 

[VinnyBagOfDonuts]

Let's say I copy a file to a location and halfway through, cancel the copying. This will not create a write hole?

 

[Sfynx]

Let's say I copy a file to a location and halfway through, cancel the copying. This will not create a write hole?

No, it won't. If you simply cancel the copy operation, all drives still get the chance to finish their writes to keep the consistent state of both data and parity.

With an operating system crash (such as a BSOD_ it should only be a problem when your operating system handles the RAID. If your RAID is handled by a hardware RAID controller, an operating system crash would still leave the controller powered up so it can update all drives to keep consistency.

A sudden power outage is the worst scenario. Hardware RAID controllers can surely handle that when they have a battery backed cache, but with software RAID it depends on the implementation. ZFS software RAID (a.k.a. RAID-Z) does not have write holes. I use it exclusively for mass file storage purposes, because no other RAID system is that advanced at the moment.

 

[VinnyBagOfDonuts]

It's built into my motherboard. I assume that's a hardware raid meaning a bsod will not cause a write hole? Thank you for all the replies!