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тАО03-03-2008 08:48 AM
тАО03-03-2008 08:48 AM
LUN Theory
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тАО03-03-2008 08:58 AM
тАО03-03-2008 08:58 AM
Re: LUN Theory
Why not continue your other thread?
Anyway, a LUN is a logical unit, see
http://en.wikipedia.org/wiki/Logical_Unit_Number
Regarding the setup you should read the manual. Get it from here
http://h20000.www2.hp.com/bizsupport/TechSupport/SupportTaskIndex.jsp?lang=en&cc=us&taskId=101&prodClassId=-1&contentType=SupportManual&docIndexId=64255&prodTypeId=18964&prodSeriesId=64112
Hope this helps!
Regards
Torsten.
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those who understand binary, and those who don't.
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тАО03-03-2008 09:00 AM
тАО03-03-2008 09:00 AM
Re: LUN Theory
(from the manual)
Many operating systems rely on the presence of LUN 0 to establish a
communication path to all LUNs on the array. Consequently, it is
recommended that the array always have LUN 0 present.
When LUN 0 is created, the array automatically creates an entry in the LUN
security table granting Write & Configure access to all hosts. This entry ensures
that all Command View SDM hosts will be able to manage the array. It is
recommended that this entry not be deleted from the table.
Because all hosts will have access to LUN 0, you may want to limit its size (10
MB) and not use it to store any critical data.
Hope this helps!
Regards
Torsten.
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тАО03-03-2008 09:59 AM
тАО03-03-2008 09:59 AM
Re: LUN Theory
LUN 0 is used for communication to the storage array only/normally. Normally it's used to have a working scsi device in place for each storage-array-controller (-port). Don't assign it as a "usable" LUN and don't put it under any Volume Manager control (do not do a pvcreate or a vxdisksetup on it).
Which LUN is the right size? If you use a "midrange storage array" like HP EVA or EMC Clariion it might be useful to use only few and large LUNs: the number of LUNs which can be presented to one and the same server is limited to e.g. 256 LUNs. Keep in mind that your Volume Manager (LVM) does not support dynamic growth of the underlying PVs (physical volumes): unless you "format" them again (loosing all data on them) you cannot resize the PV (take it off any LV, take it off the VG, do a pvcreate on it). So to grow your filesystem you have to create an additional LUN an add it to the VG, enlarge your LV by using it and then enlarge your filesystem. You will need another (free) LUN-Number for it ...
Assuming the Diskgroup-Layout on the Storage-Array is done in that way that there are only few disk groups (2 to 4) each holding a preferably large number of disks, the performance of one single LUN will be almost as good as concating 2 LUNs from 2 Diskgroups together. So I would start with as few LUNs as possible (not knowing any further parameters).
For High-End Storge like HP XP or EMC DMX the limitation of LUN-Numbers is much higher. But for other reasons it might be necessary to use more LUNs than one because of the creation policy used for small LUNs or (bigger) (Loose-)Volumes.
Regards,
Carsten
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тАО03-04-2008 05:25 PM
тАО03-04-2008 05:25 PM
Re: LUN Theory
As for HP-UX, architecturally it is typically beneficial to have more than one LUN in a Volume Group. By default, HP-UX gives each LUN (actually the device file) a "queue depth" of 8. If you have more LUNs, they are additive in nature in the VG. So, if you have 8 LUNs in a VG, you would have a queue depth of 64. Whether you need that or it would help, that up to your application. As they say your mileage may vary. But, it typically doesn't hurt. There are ways around this with some tuning, but this is the basic concept.
Cheers,
Curt
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тАО03-04-2008 06:51 PM
тАО03-04-2008 06:51 PM
Re: LUN Theory
tienna