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Re: [linux-lvm] understanding snapshot



On Thursday, January 15, 2004, at 03:45  PM, Rich Turner wrote:
[...]
what will happen to the backup process (tar for example) of a snapshot
lv when it runs out of storage?

Reads from the snapshot will return I/O errors. The backup process will likely fail.

do chunks contain the metadata for the data in the original lv?

If metadata is written to the original lv, then yes.

what is the effect of increasing/reducing the chunk size?

Depending on your write pattern, smaller chunk sizes may make the snapshot use space more slowly. (If you write even 1K to a 4 MB chunk, the whole chunk will be copied.) But it will also cause there to be more physical chunks to exist in a snapshot volume of the same size. Using LVM1 I ran into problems with snapshots eating up precious vmalloc memory, so I tend to use a large snapshot chunk size. YMMV.

Dale J. Stephenson
dalestephenson mac com




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