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745
July 14th, 2011 04:00
RLP sizing help.
I wondered if you guys could confirm i have configured my RLP with the correct size LUN's.
1st of all I have the following LUN's that are going to be MirrorView'd:
1 x 450GB
1 x 200GB
1 x 100GB
1 x 150GB
1 x 200GB
10 x 400GB
So from my understanding you work out the average size which is 340GB, and take 10% of that as the RLP LUN size, so 34GB and then multiply that by the number of LUN's x 2, so we would get 30 x 34GB LUNs, correct?
So we're going to have to create the same on the detination array for MirrorView, however that destination array has already a 1.5TB LUN that we snapshot weekly, so how would that influence the LUN sizing for the destination RLP, the average is then 412GB, so do we create 32 x 41GB LUNs? I'm concerened that the snapshot of the 1.5TB LUN will eat up a number of the LUN's that i would like to have for the MirrorView product.
Are there anyways that you can reserve RLP LUN's for certain source LUN's?
Many Thanks for you help, i hope i made my question clear!
kelleg
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4.5K Posts
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July 14th, 2011 09:00
See page 21 of the Best Practice Guide on PowerLink
http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/h1585-clariion-resvd-lun-wp.pdf
glen
BAP2
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July 14th, 2011 11:00
Hello,
"20%" is just a rule of thumb, not a requirement. Since you have an existing snapshot, you can look at the properties of the reserved LUN pool in Unisphere to understand how much reserved LUN capacity is being used by your current snapshot. You can also use Navisphere CLI naviseccli reserved -list. Take a look at this property when the snapshot is at its oldest.
For MirrorView, the size of the secondary reserved LUN is going to depend on how much you are writing and how often you are updating the mirror. MV/A will only send the unique changes, but you can easily get a worst case estimate by looking at all of the writes to the source LUNs. This can be done with Navisphere Analyzer. If you don't have an Analyzer license, and EMC employee or partner can collect the encrypted files (.naz) and assist you with the analysis. You may have these files already if the solution was approved by EMC's Solution Validation Center. In Analyzer, you can get an average write bandwidth over the period between updates or look at the I/O Distribution Detail chart to see how many writes of each I/O size occur per Analyzer polling period. Dump them to a spreadsheet to add them up.
Based on the actual numbers from your environment, you can decide what you are comfortable with. So if it turns out you are only writing 1-2% of the total capacity between updates, perhaps you target 10% for Reserved LUN space. You should account for any bursts in activity or extended link outages that may result in larger updates.
Last but not least, I don't know what array model you're using, but I think you tagged this request as CX4, so you have at least a 128 reserved LUN limit. You could spread your reserved LUN capacity over a larger number of reserved LUNs, say 50, and let the array allocate as necessary. You have to have at least 1 reserved LUN per mirror or snap source LUN, but you can have multiple reserved LUNs assigned to a source. Based on the number of replicas you listed, you have flexibility in reserved LUN size, because you're not pressed up against any hard limits.
Regards,
Bruce
christopher_ime
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July 21st, 2011 22:00
>> Are there anyways that you can reserve RLP LUN's for certain source LUN's?
Just wanted to address one unanswered question. No, you do not have the ability to map a specific LUN in the RLP to a specific source LUN. They are allocated as needed from the (shared) pool of LUNs.
Well... then again, for just the initial LUN from the RLP that is assigned you could accomplish this as follows:
a) Add only desired LUN to the RLP
b) Create your MirrorView/A, Incremental SAN Copy, or SnapView session of the source LUN you want assigned
Then you can continue this process one pair at a time and using the fact that each source LUN is paired with a unique LUN in the RLP, this would accomplish what you inquired about. Again, this would work only for the initial LUN that is assigned.
Then again, it is not worth the effort and you'd just size your LUNs as already discussed and ensure there are enough of the shared resources to distribute as needed.