[linux-lvm] understanding snapshot
Dale J. Stephenson
dalestephenson at mac.com
Thu Jan 15 23:52:01 UTC 2004
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 at mac.com
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