Actually - I don't understand why minra would not be possibly enabled on destination but not source. I understand that these are volume-level options, but it would make more sense to me to have an option to override that particular setting on a destination volume due to issues just as you've described here.
Smells like a great RFE to me :)
Glenn
-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Peter D. Gray Sent: Thursday, August 31, 2006 7:53 PM To: toasters@mathworks.com Subject: Re: when to use minra ?
Thanks for the replies. Some background on this question.
I have 2 filers used for email storage (NFS, attached to 2 mirapoint mail stores). They have lots of small files. I am mirroring these 2 filers to an R200 for backup, but I also take tape copies via NDMP every 30 days or so. The volumes contain about 350GB each of actual data, excluding snapshots, and 5 million files.
My NDMP tape backups from the R200 are pretty slow. I average about 2 MBytes per sec. Note that backups of other volumes on te R200 work really well, so there is no problem on the R200 or the network.
I saw the comment that turning off minra can have a big impact on backup performance so I thought I would try it. But discovered that the setting would have to be changed on the mirror source which is not so good (maybe).
It would be nice if that setting could be changed on the mirror target but not the source, but I can see why that not possible.
So, I wondered if I could justify setting minra on on the source volumes but would need some way to predict the impact.
It sounds like turing on minra is not usually a good idea, so I guess I am stuck with slow NDMP backups.
Just out of interest, does anybody understand why minra has an impact on backup speed. I assume the read ahead does not go past end of file but that is the only explanation I can think of as to why it would have an impact?
Regards, pdg
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To summerise the thread so far and reply to some suggestions:
1) I should test minra off on the mirror target while doing a a backup. Good idea, I will try this. 2) minra can not be set on the target unless the mirror is broken or it is set on the source. This is just a fact of life at the moment. 3) the read ahead algorithm tries to speed things up for sequential reads. OK, thats fine, but backups are sequential reads, so you might think that turning on minra would make things worse for backups. But some peopel report the opposite. I have not seen a analysis from anyone that explains why minra has any effect on backups. Can somebody from netapp comment on this? Is the backup multithreaded? If not, I can imagine it being real slow for lots of small files no matter what you did. 4) People asked for details on the configuration. Its ONTAP 7.0.4, 3 shelves on the R200, single aggregate, 2 raid groups, 20 drives in each raid group, raid DPP, gig ethernet back to the backup machine, switched, not routed, NDMP in 3 way mode. Nice fast SUN running the backup software (netvault), backup goes to disk. Whew! For my database volumes I get 10-20 MBytes per sec sustained transfers. Not suprising, nice large files. For my other volumes, I get varying rates, but in all cases as the number of files goes up and the file size goes down by backup speed goes down. The mail volumes are obviously the worst case. The most interesting thing to me is item 3 above.
Regards, pdg
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Glenn Walker -
Peter D. Gray