On 03/03/2013 10:19 AM, Adam Goryachev wrote: > Phil Turmel <philip@xxxxxxxxxx> wrote: > >> On 03/02/2013 04:15 AM, Stan Hoeppner wrote: >>> On 3/1/2013 10:06 AM, Adam Goryachev wrote: >> >>>> 15) "Make sure all LVs are aligned to the underlying md device >>>> geometry. This will eliminate any possible alignment issues." >>>> What does this mean? The drive partitions are now aligned properly, >>>> but how does LVM allocate the blocks for each LV, and how do I >>>> ensure it does so optimally? How do I even check this? >>> >>> I'm not an LVM user so I can't give you command lines. But what I >>> can tell you follows, and it is somewhat critical to RMW performance, >>> more for rust but also for SSD to a lesser degree. >> Run "dmsetup table" and look at the start sectors for your volumes: >> Fast-Root: 0 314572800 linear 9:3 3072 >> This volume starts at sector 3072 (1.5MB) on /dev/sda3. So the volume >> alignment within LVM is 512K. > > I see this (for the first LV) > vg0-hostname: 0 204808192 linear 147:2 512 > So, I'm guessing mine is starting at 512, and is also aligned at 512k ? Not quite. Those size and offset numbers are shown in *sectors*, so you have 256k alignment. But that's exactly the minimum you need to match your raid5 chunk size, so you are good for the moment. > Also, pvdisplay tells me the PE Size is 4M, so I'm assuming that regardless of how the LV's are arranged, they will always be 512k aligned? 256k, but yeah. > So, is that enough to be sure that this is not an issue? It looks to me like you are good on alignment. Phil -- 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
