Correct, but were not using reallocate here for its _intended_ purpose.
Were using it for what it happens to do as a benefit to wafl free space management.
On Tue, Mar 20, 2012 at 7:00 AM, Fletcher Cocquyt fcocquyt@stanford.eduwrote:
I had a case open with Netapp and the engineer came back with this:
Data ONTAP® 7.3 System Administration Guide:****
https://now.netapp.com/NOW/knowledge/docs/ontap/rel7351/pdfs/ontap/sysadmin....
*What a reallocation scan is, Page 315*
“A file reallocation scan using reallocate start or reallocate start -p does not rearrange blocks that are shared between files by deduplication on deduplicated volumes. Because a file reallocation scan does not predictably improve read performance when used on deduplicated volumes, it is best not to perform file reallocation on deduplicated volumes. If you want your files to benefit from a reallocation scan, store them on volumes that are not enabled for deduplication.”
--
We ended up reallocating (in effect) when we upgraded to 8.1 using data motion to migrate to fresh aggregates (btw 2 clusters) But I'd be interested to know if you get a different answer (and net benefit from reallocation on a dedup'ed volume)
thanks
On Mar 19, 2012, at 11:58 PM, Mathew Kilham wrote:
Hi Jeff & Toasters,
Yup, its the best you can do at this time.
Thanks.
Do you specifically know that this will work as intended though? e.g., as per my original e-mail: "will this actually result in a physical reallocate being performed, or will the deduped blocks still be skipped because they're already de-duplicated, regardless of whether dedupe is enabled for new data on the volume or not?"
I'm re-querying because I struggle to see why de-dupe being on/off for new blocks would affect the ability to reallocate, whereas I can imagine scenarios where blocks /already/ being deduplicated could affect the ability to reallocate.
DO NOT do a reallocate -A.
DO NOT.
Thanks for that Jeff - we'll be very careful to avoid the -A option :-)
Cheers, Matt
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