On Wed, 2005-08-24 at 10:24 +0200, Mirko Benz wrote: > Hello, > > We have recently tested Linux 2.6.12 SW RAID versus HW Raid. For SW Raid > we used Linux 2.6.12 with 8 Seagate SATA NCQ disks no spare on a Dual > Xeon platform. For HW Raid we used a Arc-1120 SATA Raid controller and a > Fibre Channel Raid System (Dual 2 Gb, Infortrend). > > READ SW:877 ARC:693 IFT:366 > (MB/s @64k BS using disktest with raw device) > > Read SW Raid performance is better than HW Raid. The FC RAID is limited > by the interface. > > WRITE SW:140 ARC:371 IFT:352 > > For SW RAID 5 we needed to adjust the scheduling policy. By default we > got only 60 MB/s. SW RAID 0 write performance @64k is 522 MB/s. how u test and get these number? what is u raid5 configuration? chunk size? > > Based on the performance numbers it looks like Linux SW RAID reads every > data element of a stripe + parity in parallel, performs xor operations > and than writes the data back to disk in parallel. > > The HW Raid controllers seem to be a bit smarter in this regard. When > they encounter a large write with enough data for a full stripe they > seem to spare the read and perform only the xor + write in parallel. > Hence no seek is required and in can be closer to RAID0 write performance. this is stripe write and linux MD have this. > > We have an application were large amounts of data need to be > sequentially written to disk (e.g. 100 MB at once). The storage system > has an USV so write caching can be utilized. > > I would like to have an advice if write performance similar to HW Raid > controllers is possible with Linux or if there is something else that we > could apply. > > Thanks in advance, > Mirko > > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
