LVM Question
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Ok this might be a dumb question. What's a scenario where you would span a volume group over multiple disks? The only thing I could think of was needing extra space, but why not just increase the size of your disk?
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I just thought of this. Possibly MBR disk size lmitations?
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@johnhooks said:
The only thing I could think of was needing extra space, but why not just increase the size of your disk?
There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.
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@scottalanmiller said:
@johnhooks said:
The only thing I could think of was needing extra space, but why not just increase the size of your disk?
There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.
What's the advantage to doing that over RAID 0 and then making one PV?
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@johnhooks said:
What's the advantage to doing that over RAID 0 and then making one PV?
Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."
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@scottalanmiller said:
@johnhooks said:
What's the advantage to doing that over RAID 0 and then making one PV?
Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."
I didn't realize it was more reliable than RAID 0. Thanks!
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@scottalanmiller said:
@johnhooks said:
The only thing I could think of was needing extra space, but why not just increase the size of your disk?
There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.
@scottalanmiller said:
@johnhooks said:
The only thing I could think of was needing extra space, but why not just increase the size of your disk?
There are a great many cases when you cannot just increase the size of your disks. It is actually extremely common in the enterprise space that many small LUNs be handed to the system and LVM be expected to bind them into a single storage unit.
Plus I guess if you're not in control of the Hypervisor then you'd have to make due with what you're given.
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@johnhooks said:
@scottalanmiller said:
@johnhooks said:
What's the advantage to doing that over RAID 0 and then making one PV?
Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."
I didn't realize it was more reliable than RAID 0. Thanks!
It's not great, the filesystem tends to be unhappy when parts disappear. But if you have 100 slices and one vanishes, likely only a few files will be impacted rather than everything. Not always, but safer at least.
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@scottalanmiller said:
@johnhooks said:
@scottalanmiller said:
@johnhooks said:
What's the advantage to doing that over RAID 0 and then making one PV?
Reliability. If one slice fails, RAID 0 would hose the full filesystem. With a span there is a lot less "one blip spells total disaster."
I didn't realize it was more reliable than RAID 0. Thanks!
It's not great, the filesystem tends to be unhappy when parts disappear. But if you have 100 slices and one vanishes, likely only a few files will be impacted rather than everything. Not always, but safer at least.
That's kind of awesome. I didn't realize it was that much more reliable.
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Also if one slice is slow and the others are fast, you don't have to wait on the one to put blocks together. So temperamental delays are less impactful.
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And if you have mismatched sizes you would lose space with RAID 0. And can't grow RAID 0 either.
Ha I knew it was a dumb question.
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@johnhooks said:
And if you have mismatched sizes you would lose space with RAID 0. And can't grow RAID 0 either.
Ha I knew it was a dumb question.
Very true as well.
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I :heart: LVM
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LVM is awesome, it is a great tool.
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@StrongBad said:
LVM is awesome, it is a great tool.
I use it all the time. Snapshots are awesome. I've just never needed to use multiple disks and didn't think of the above scenarios when you would have multiple PVs.
