From b55d752a8dd903aaaeacaeaecb0ffbfa294a214f Mon Sep 17 00:00:00 2001 From: Andreas Dilger Date: Tue, 18 Apr 2017 20:11:40 -0600 Subject: [PATCH] LU-9348 proc: describe brw_size limits better Add a description of the brw_size limits (minimum and maximum values). Signed-off-by: Andreas Dilger Change-Id: I03ea6bfedd971a510d2861deae8dafaa6fbe4f82 Reviewed-on: https://review.whamcloud.com/26726 Tested-by: Jenkins Reviewed-by: Joseph Gmitter --- LustreTuning.xml | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/LustreTuning.xml b/LustreTuning.xml index 7caf0e6..b3854f0 100644 --- a/LustreTuning.xml +++ b/LustreTuning.xml @@ -1495,15 +1495,26 @@ ldlm.namespaces.filter-fsname-*. Beginning with Lustre 2.9, Lustre is extended to support RPCs up to 16MB in size. By enabling a larger RPC size, fewer RPCs will be required to transfer the same amount of data between clients and - servers. With a larger RPC size, the OST can submit more data to the + servers. With a larger RPC size, the OSS can submit more data to the underlying disks at once, therefore it can produce larger disk I/Os to fully utilize the increasing bandwidth of disks. - At client connecting time, clients will negotiate with - servers for the RPC size it is going to use. - A new parameter, brw_size, is introduced on - the OST to tell the client the preferred IO size. All clients that + At client connection time, clients will negotiate with + servers what the maximum RPC size it is possible to use, but the + client can always send RPCs smaller than this maximum. + The parameter brw_size is used on the OST + to tell the client the maximum (preferred) IO size. All clients that talk to this target should never send an RPC greater than this size. + Clients can individually set a smaller RPC size limit via the + osc.*.max_pages_per_rpc tunable. + + The smallest brw_size that can be set for + ZFS OSTs is the recordsize of that dataset. This + ensures that the client can always write a full ZFS file block if it + has enough dirty data, and does not otherwise force it to do read- + modify-write operations for every RPC. + +
Usage In order to enable a larger RPC size, @@ -1530,7 +1541,7 @@ ldlm.namespaces.filter-fsname-*. client$ lctl conf_param fsname-OST*.osc.max_pages_per_rpc=16M The brw_size of an OST can be changed on the fly. However, clients have to be remounted to - renegotiate the new RPC size. + renegotiate the new maximum RPC size.
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