On Thu, Jun 19, 2008 at 9:49 AM, Wendy Cheng <s.wendy.cheng@xxxxxxxxx> wrote: > Terry wrote: >> >> On Tue, Jun 17, 2008 at 5:22 PM, Terry <td3201@xxxxxxxxx> wrote: >> >>> >>> On Tue, Jun 17, 2008 at 3:09 PM, Wendy Cheng <s.wendy.cheng@xxxxxxxxx> >>> wrote: >>> >>>> >>>> Hi, Terry, >>>> >>>>> >>>>> I am still seeing some high load averages. Here is an example of a >>>>> gfs configuration. I left statfs_fast off as it would not apply to >>>>> one of my volumes for an unknown reason. Not sure that would have >>>>> helped anyways. I do, however, feel that reducing scand_secs helped a >>>>> little: >>>>> >>>>> >>>> >>>> Sorry I missed scand_secs (was mindless as the brain was mostly occupied >>>> by >>>> day time work). >>>> >>>> To simplify the view, glock states include exclusive (write), share >>>> (read), >>>> and not-locked (in reality, there are more). Exclusive lock has to be >>>> demoted (demote_secs) to share, then to not-locked (another demote_secs) >>>> before it is scanned (every scand_secs) to get added into reclaim list >>>> where >>>> it can be purged. Between exclusive and share state transition, the file >>>> contents need to get flushed to disk (to keep file content cluster >>>> coherent). All of above assume the file (protected by this glock) is >>>> not >>>> accessed (idle). >>>> >>>> You hit an area that GFS normally doesn't perform well. With GFS1 in >>>> maintenance mode while GFS2 seems to be so far away, ext3 could be a >>>> better >>>> answer. However, before switching, do make sure to test it thoroughly >>>> (since >>>> Ext3 could have the very same issue as well - check out: >>>> http://marc.info/?l=linux-nfs&m=121362947909974&w=2 ). >>>> >>>> Did you look (and test) GFS "nolock" protocol (for single node GFS)? It >>>> bypasses some locking overhead and can be switched to DLM in the future >>>> (just make sure you reserve enough journal space - the rule of thumb is >>>> one >>>> journal per node and know how many nodes you plan to have in the >>>> future). >>>> >>>> -- Wendy >>>> >>> >>> Good points. I could try the nolock feature I suppose. Not quite >>> clear on how to reserve journal space. I forgot to post the cpu time, >>> check out this: >>> >>> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND >>> 4822 root 10 -5 0 0 0 S 1 0.0 2159:15 dlm_recv >>> 4820 root 10 -5 0 0 0 S 1 0.0 368:09.34 dlm_astd >>> 4821 root 10 -5 0 0 0 S 0 0.0 153:06.80 dlm_scand >>> 3659 root 10 -5 0 0 0 S 0 0.0 134:40.14 scsi_wq_4 >>> 4823 root 11 -5 0 0 0 S 1 0.0 109:33.33 dlm_send >>> 367 root 10 -5 0 0 0 S 0 0.0 103:33.74 kswapd0 >>> >>> gfs_glockd is further below so not so concerned with that right now. >>> It appears turning on nolock would do the trick. The times aren't >>> extremely accurate because I have failed this cluster between nodes >>> while testing. >>> >>> >> >> Here is some more testing information.... >> >> I created a new volume on my iscsi san of 1 TB and formatted it for >> ext3. I then used dd to create a 100G file. This yielded roughly 900 >> Mb/sec. I then stopped my application and did the same thing with an >> existing GFS volume. This gave me about 850 Kb/sec. This isn't an >> iscsi issue. This appears to be a load issue and the number of I/O >> occurring on these volumes. That said, I would expect that performing >> the changes I did would result in a major performance improvement. >> Since it didn't, what are my other points I could consider? If its a >> GFS issue, ext3 is the way to go. Maybe even switch to using >> active-active on my NFS cluster. If its a backend disk issue, I >> would expect to see the throughput on my iscsi link (bond1) be fully >> utilized. Its not. Could I be thrashing the disks? This is an iscsi >> san with 30 sata disks. Just bouncing some thoughts around to see if >> anyone has any more thoughts. >> >> > > Really need to focus on my day time job - its worload has been climbing ... > but can't help to place a quick comment here .. > > The 900 MB/s vs. 850 KB/s difference looks like a caching issue - that is, > for 900 MB/s, it looks like the data was still lingering in the system cache > while in 850 KB/s case, the data might already hit disk. Cluster filesystem > normally syncs more by its nature. In general, ext3 does perform better in > single node environment but the difference should not be as big as above. > There are certainly more tuning knobs available (such as journal size and/or > network buffer size) to make GFS-iscsi "dd" run better but it is pointless. > To deploy a cluster filesystem for production usage, the tuning should not > be driven by such a simple-mind command. You also have to consider the > support issues when deploying a filesystem. GFS1 is a little bit out of date > and any new development and/or significant performance improvements would > likely be in GFS2, not in GFS1. Research GFS2 (googling to see how other > people said about it) to understand whether its direction fits your need (so > you can migrate from GFS1 to GFS2 if you bump into any show stopper in the > future). If not, ext3 (with ext4 actively developed) is a fine choice if I > read your configuration right from previous posts. > > -- Wendy I wrote off the difference between ext3 and gfs performance with my simple dd command as nothing. I wanted to ensure I wasn't seeing some other issue. I am happy with 800-900 regardless of the filesystem. I'm going to see if I can get some performance metrics off the SAN and go from there. -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
