On 9/26/2013 4:58 PM, Dave Chinner wrote: > On Thu, Sep 26, 2013 at 04:22:30AM -0500, Stan Hoeppner wrote: >> On 9/26/2013 3:55 AM, Stewart Webb wrote: >>> Thanks for all this info Stan and Dave, >>> >>>> "Stripe size" is a synonym of XFS sw, which is su * #disks. This is the >>>> amount of data written across the full RAID stripe (excluding parity). >>> >>> The reason I stated Stripe size is because in this instance, I have 3ware >>> RAID controllers, which refer to >>> this value as "Stripe" in their tw_cli software (god bless manufacturers >>> renaming everything) >>> >>> I do, however, have a follow-on question: >>> On other systems, I have similar hardware: >>> 3x Raid Controllers >>> 1 of them has 10 disks as RAID 6 that I would like to add to a logical >>> volume >>> 2 of them have 12 disks as a RAID 6 that I would like to add to the same >>> logical volume >>> >>> All have the same "Stripe" or "Strip Size" of 512 KB >>> >>> So if I where going to make 3 seperate xfs volumes, I would do the >>> following: >>> mkfs.xfs -d su=512k sw=8 /dev/sda >>> mkfs.xfs -d su=512k sw=10 /dev/sdb >>> mkfs.xfs -d su=512k sw=10 /dev/sdc >>> >>> I assume, If I where going to bring them all into 1 logical volume, it >>> would be best placed to have the sw value set >>> to a value that is divisible by both 8 and 10 - in this case 2? >> >> No. In this case you do NOT stripe align XFS to the storage, because >> it's impossible--the RAID stripes are dissimilar. In this case you use >> the default 4KB write out, as if this is a single disk drive. >> >> As Dave stated, if you format a concatenated device with XFS and you >> desire to align XFS, then all constituent arrays must have the same >> geometry. >> >> Two things to be aware of here: >> >> 1. With a decent hardware write caching RAID controller, having XFS >> alined to the RAID geometry is a small optimization WRT overall write >> performance, because the controller is going to be doing the optimizing >> of final writeback to the drives. >> >> 2. Alignment does not affect read performance. > > Ah, but it does... > >> 3. XFS only performs aligned writes during allocation. > > Right, and it does so not only to improve write performance, but to > also maximise sequential read performance of the data that is > written, especially when multiple files are being read > simultaneously and IO latency is important to keep low (e.g. > realtime video ingest and playout). Absolutely correct, as Dave always is. As my workloads are mostly random, as are those of others I consult in other fora, I sometimes forget the [multi]streaming case. Which is not good, as many folks choose XFS specifically for [multi]streaming workloads. My remarks to this audience should always reflect that. Apologies for my oversight on this occasion. >> What really makes a difference as to whether alignment will be of >> benefit to you, and how often, is your workload. So at this point, you >> need to describe the primary workload(s) of your systems we're discussing. > > Yup, my thoughts exactly... > > Cheers, > > Dave. > -- Stan _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
