Hi folks: I built a RAID0 stripe across two large hardware RAID cards (identical cards/driver). What I am finding is that direct IO is about the performance I expect (2x the single RAID card) while buffered IO is about the same as the performance of a single RAID card. This is true across chunk sizes of 64 through 4096k, with an xfs file system. This is a 2.6.23.14 kernel. I tried 2.6.24.2, and there the direct IO was the same speed as the buffered IO on one RAID card, even though the RAID0 striped across 2 RAID cards. There appears to be some issue with this combination of RAID0, buffer cache, and the driver. Breaking the raid in 2, and performing the same tests on each RAID card results in the expected performance during buffered io and direct IO. Is there something I can do to tune how the raid0 driver deals with buffer cache? Standard vm-tweaking yields modest changes, but I am not convinced the issue is there. It looks like the raid0 driver is serializing something in buffer cache access. Does this make sense? For small drives and SATA drivers, I see the "expected" RAID0 behavior. Is it possible that with very large or very fast devices that there is some sort of buffer serialization? Clues and guidance are requested. Thanks! Joe - 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
