Messages in this thread | | | Date | Thu, 27 Jan 2011 18:09:58 -0800 (PST) | From | david@lang ... | Subject | Re: xfs: very slow after mount, very slow at umount |
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On Thu, 27 Jan 2011, Stan Hoeppner wrote:
> david@lang.hm put forth on 1/27/2011 2:11 PM: > >> how do I understand how to setup things on multi-disk systems? the documentation >> I've found online is not that helpful, and in some ways contradictory. > > Visit http://xfs.org There you will find: > > Users guide: > http://xfs.org/docs/xfsdocs-xml-dev/XFS_User_Guide//tmp/en-US/html/index.html > > File system structure: > http://xfs.org/docs/xfsdocs-xml-dev/XFS_Filesystem_Structure//tmp/en-US/html/index.html > > Training labs: > http://xfs.org/docs/xfsdocs-xml-dev/XFS_Labs/tmp/en-US/html/index.html
thanks for the pointers.
>> If there really are good rules for how to do this, it would be very helpful if >> you could just give mkfs.xfs the information about your system (this partition >> is on a 16 drive raid6 array) and have it do the right thing. > > If your disk array is built upon Linux mdraid, recent versions of mkfs.xfs will > read the parameters and automatically make the filesystem accordingly, properly. > > mxfs.fxs will not do this for PCIe/x hardware RAID arrays or external FC/iSCSI > based SAN arrays as there is no standard place to acquire the RAID configuration > information for such systems. For these you will need to configure mkfs.xfs > manually. > > At minimum you will want to specify stripe width (sw) which needs to match the > hardware stripe width. For RAID0 sw=[#of_disks]. For RAID 10, sw=[#disks/2]. > For RAID5 sw=[#disks-1]. For RAID6 sw=[#disks-2]. > > You'll want at minimum agcount=16 for striped hardware arrays. Depending on the > number and spindle speed of the disks, the total size of the array, the > characteristics of the RAID controller (big or small cache), you may want to > increase agcount. Experimentation may be required to find the optimum > parameters for a given hardware RAID array. Typically all other parameters may > be left at defaults.
does this value change depending on the number of disks in the array?
> Picking the perfect mkfs.xfs parameters for a hardware RAID array can be > somewhat of a black art, mainly because no two vendor arrays act or perform > identically.
if mkfs.xfs can figure out how to do the 'right thing' for md raid arrays, can there be a mode where it asks the users for the same information that it gets from the kernel?
> Systems of a caliber requiring XFS should be thoroughly tested before going into > production. Testing _with your workload_ of multiple parameters should be > performed to identify those yielding best performance.
<rant> the problem with this is that for large arrays, formatting the array and loading it with data can take a day or more, even before you start running the test. This is made even worse if you are scaling up an existing system a couple orders of magnatude, because you may not have the full workload available to you. Saying that you should test out every option before going into production is a cop-out. The better you can test it, the better off you are, but without knowing what the knobs do, just doing a test and twiddling the knobs to do another test isn't very useful. If there is a way to set the knobs in the general ballpark, then you can test and see if the performance seems adaquate, if not you can try teaking one of the knobs a little bit and see if it helps or hurts. but if the knobs aren't even in the ballpark when you start, this doesn't help much. </rant>
David Lang
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