On Tue, Mar 4, 2014 at 1:29 AM, Peter Grandi <pg@xxxxxxxxxxxxxxxxxxxx> wrote: >> [ ... ] Which tool settings? [ ... ] > > As to this, how are the 8KiB writes aligned? To 1KiB? 4KiB? > 8KiB? To something else? They were 4Kb aligned. Looking at the code, I don't think it matters much; if I had them them 8K aligned, it would still be required to load/update 2 stripe-heads for each write. > > Is there any other activity on the same physical disks given > that the RAID members seem to be LVs? They are device-mapper devices (but not LVs), and there was no other activity. The device-mappers lead to drives behind MegaRAID write-back caching. (Something tells me you will find this funny at best, but as I mentioned, I am just trying to understand how much write latency MD can add on top of drives latencies). > > Also what's the size of those LV members of the MD set? It may > be quite small... Each one is 560GB. The whole MD usable space is ~2.2TB, so with a random workload over such huge capacity, MD stripe cache cannot help anyways. You need to load and update new stripe-heads every write. This was the purpose of the test. In my case, I had 1024 stripe-heads, while only up to 500 of them were active. Alex. > -- > 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
