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[dm-devel] Performance Question



Hello all,

we are about to configure a new storage system that utilizes the Nexenta OS with sparsely allocated ZVOLs.  We wish to present 4TB of storage to a Linux system that has four NICs available to it. We are unsure whether to present one large ZVOL or four smaller ones to maximize the use of the NICs available to us.  We have set rr_min_io to 100 which we have found offers a good level of performance.  Though this raises an interesting question; that the multipath.conf man pages says that the rr_min_io parameter is the number of IOs across the whole path group before a switch is made to the next path. What constitutes a single IO operation ? A user opens a file for read access, one IOP to open the file, IOsX to read the contents, and another to close ? Do each of those SCSI operations happen on the same path ie. on the same block device ? If a second user comes along and requests data from the same block device do they happen on the same path or the next one in the path group ? We imagine that they will all happen on the same path until rr_min_io is reached and it switches over to the next path.

We are trying to squeeze out the maximum performance from our system and we are unable to max out our 4 x 1Gbe interfaces. Any thoughts on how we can improve our performance ?
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Thanks, Phil


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