> > And finally the SAS drive. For CEPH I don't see this drive making much > sense. Most manufacturers enterprise SATA drives are identical to the SAS > version with just the different interface. Performance seems identical in > all comparisons I have seen, apart from the fact that SATA can only queue up > to 32 IO's, not sure how important this is? But they also command a price > premium. > Anecdotal: I got a good deal on some new systems, including WD Nearline SAS disks. It wasn't amazing, but the whole system was cheaper than me manually assembling a SuperMicro with some HGST SATA disks. The SATA nodes have a battery backed RAID0 setup. The SAS nodes are using a SAS HBA (no write cache). All nodes' journals are the same model Intel SATA SSD, with no write caching. My load test was snapshot trimming, and I noticed it from watching atop. Completely quantifiable and repeatable ;-). The SAS disks would consistently finish sooner than the SATA disks. For a rmsnap that took ~2 hours to trim, the SAS disks would finish up about 15 minutes sooner. Regardless of uneven data distribution, all SAS disks were completely done trimming before the first SATA disk started to ramp down it's IOPS. This is something I just noticed, so I haven't (yet) spent any time trying to actually quantify. I only noticed when the load was high enough to make cluster completely unresponsive. I have no idea if the difference will show up under normal loads. I'm not even sure how I'm going to quantify this, since the lack of write cache on the SAS disks makes the graphs much harder to compare. So far, the best I can say is that the SAS disks are "faster", even without a write cache. _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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