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JoseGMSK
1 Copper

VPlex Mobility Jobs Transfer-Speed?? Help??

I'm using the vplex to migrate data from one array to another and typically set it to 1M as the transfer size.

My question is, and i'm hoping someone out there could explain this to me, at 1M im seeing the reads and write on the target array as 65MBs... If i change it to 512K the reads and writes on the array drop to 13MBs.

I'm expecting 1M to transfer at 1M or is there something else i'm not accounting for?

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driscd1
1 Copper

Re: VPlex Mobility Jobs Transfer-Speed?? Help??

"transfer-size" is a size used internally by the VPLEX migration function.  It does not map 1:1 to, nor define, a rate that you would see on the array side, such as 65 MB/s or 13 MB/s.  In fact, any rate you see (unless very carefully filtered) might include other production I/O occurring in addition to the migration (rebuild) I/O.  Our performance advice is to typically start with small "transfer_size" and ensure there is no negative impact to other production I/O, and if not, to carefully increase it.   Starting with a large 1M transfer_size (or larger), while perhaps optimal for erducing the overall duration of the igration, potentially could impact other smaller production I/Os competing for the same bandwidth.

From the Admin Guide :

About transfer-size

Transfer-size is the size of the region in cache used to service the migration. The area is globally locked, read at the source, and written at the target.

Transfer-size can be as small 40 K, as large as 128 M, and must be a multiple of 4 K. The default recommended value is 128 K.

A larger transfer-size results in higher performance for the migration, but may negatively impact front-end I/O. This is especially true for VPLEX Metro migrations.

A smaller transfer-size results in lower performance for the migration, but creates less impact on front-end I/O and response times for hosts.

Set a large transfer-size for migrations when the priority is data protection or migration performance.Set a smaller transfer-size for migrations when the priority is front-end storage response time.

Factors to consider when specifying the transfer-size:

  • For VPLEX Metro configurations with narrow inter-cluster bandwidth, set the transfer size lower so the migration does not impact inter-cluster I/O.
  • The region specified by transfer-size is locked during migration. Host I/O to or from that region is held. Set a smaller transfer-size during periods of high host I/O.
  • When a region of data is transferred, a broadcast is sent to the system. Smaller transfer-size mean more roadcasts, slowing the migration.

Hope this helps!

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