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If one disk fails i loose everything?

linux-lvm Andrew Burgess 4 participants 4 messages Dec 13, 2005 – Dec 18, 2005

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#0 lore raw
Quoted 3 lines

Good discussion....the need to protect data under various contingencies is why I use raid5 sets as the PVs. You can lose up to two and keep your data, hot add, have spares, etc.

You mean raid6

#1 lore raw
Quoted 12 lines · Andrew Burgess
Quoted 2 lines

Good discussion....the need to protect data under various contingencies is why I use raid5 sets as the PVs. You can lose up to two and keep your data, hot add, have spares, etc.

You mean raid6

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Actually I meant raid 5 based on actual 2 disk dropouts experienced on test systems and the LVM data was still available. Probably lucky. Thanks for the note.

#2 lore raw

It really shouldn't work that way. RAID 5 is based on XOR, and I'm pretty sure XOR can only recover from a single-number failure.

-But-, if you had a hot spare or warm spare configured, then it would've been possible for one drive to die, the RAID 5 to be resync'd, another drive to die, and then still be OK.

Quoted 25 lines · Old Fart
Quoted 5 lines · Andrew Burgess
Quoted 4 lines

Good discussion....the need to protect data under various contingencies is why I use raid5 sets as the PVs. You can lose up to two and keep your data, hot add, have spares, etc.

Quoted 9 lines

You mean raid6

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Actually I meant raid 5 based on actual 2 disk dropouts experienced on test systems and the LVM data was still available. Probably lucky. Thanks for the note.

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#3 lore raw
Quoted 4 lines · Dan Stromberg

It really shouldn't work that way. RAID 5 is based on XOR, and I'm pretty sure XOR can only recover from a single-number failure.

-But-, if you had a hot spare or warm spare configured, then it would've
been possible for one drive to die, the RAID 5 to be resync'd, another drive to die, and then still be OK.

Correct. One thing to keep in mind when doing these sort of things is that drives from the same manufacturer and lot are more like to fail around the same time than random drives. We've had two drives fail within a week of each other in the same raid array multiple times. I've had a couple of raid arrays where it felt like I spent every other week for six months doing some part of a drive replacement and ending up replacing the whole array my the time its done. Now if I have two drives fail in an array in short I proactively replace the entire thing. Don't forget the I in raid means you're trying to make cheap sh*t reliable.

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