Folks - my apologies if this sounds like a FAQ but alas a search of the HOWTO and the list archives did not turn up anything along these lines... I am trying to confirm by inspection (rather than guessing based on behaviour) that a LV created with two stripes _is_ in fact striping rather than just mapping LEs to PEs in a linear fashion. I have tested both LVM 1.0.3 (SuSE 8.0) and LVM 1.0.5 (SuSE 9.0) and in both cases am left confused/annoyed. According to the HOWTO: http://www.tldp.org/HOWTO/LVM-HOWTO/mapmode.html there are two mapping modes; presumably one gets linear mapping by default, unless you explicitly ask for 'n' stripes with the '-i' param to 'lvcreate', correct? I have a number of LVs, all of which are supposedly striped (ie., were created with '-i' and 'cat /proc/lvm/global' shows a status of 'AWDS2' for all LVs) yet when I run 'lvdisplay -v' to look at the logical-to-physical mapping, it is clear that the first 'n' LEs are on the first PV whilst the second 'n' LEs are on the second PV (ie., just like the description of linear mapping in the HOWTO). Here's where my mind really gets screwed-up - if I throw data at the LVs, the read/write pattern tends to indicate that the striping _is_ working, which then contradicts the mapping that 'lvdisplay -v' shows! What's happening? Are LEs always mapped to PEs in a linear fashion whilst striping occurs at some lower (per-chunk-of-an-LE) layer? If so, is it possible to run a command and confirm that mapping (so that file system behaviour is deterministic, rather than just hoping that LVM is doing precisely what you requested)? Is the 'lvdisplay -v' just wrong? If not, how does it determine what PV/PE to display for any given LE if in reality each LE is spread over multiple PVs/PEs?? Some selected command output below to hopefully better illustrate the situation. Any/all assistance welcomed. Thanks.. # cat /proc/lvm/global | egrep -v '^$' LVM module LVM version 1.0.3(19/02/2002) Total: 1 VG 2 PVs 6 LVs (6 LVs open 6 times) Global: 304734 bytes malloced IOP version: 10 10:23:00 active VG: lvg [2 PV, 6 LV/6 open] PE Size: 4096 KB Usage [KB/PE]: 76292096 /18626 total 76292096 /18626 used 0 /0 free PVs: [AA] hda3 38146048 /9313 38146048 /9313 0 /0 [AA] hdc3 38146048 /9313 38146048 /9313 0 /0 LVs: [AWDS2 ] usr 16777216 /4096 1x open [AWDS2 ] var 18874368 /4608 1x open [AWDS2 ] opt 16777216 /4096 1x open [AWDS2 ] home 4194304 /1024 1x open [AWDS2 ] src 11321344 /2764 1x open [AWDS2 ] tmp 8347648 /2038 1x open # lvdisplay -v /dev/lvg/home | egrep -v '^$' --- Logical volume --- LV Name /dev/lvg/home VG Name lvg LV Write Access read/write LV Status available LV # 4 # open 1 LV Size 4 GB Current LE 1024 Allocated LE 1024 Stripes 2 Stripe size (KByte) 16 Allocation next free Read ahead sectors 10000 Block device 58:3 --- Distribution of logical volume on 2 physical volumes --- PV Name PE on PV reads writes /dev/hda3 512 33 18 /dev/hdc3 512 34 22 --- logical volume i/o statistic --- 67 reads 40 writes --- Logical extents --- LE PV PE reads writes 00000 /dev/hda3 06400 32 18 00001 /dev/hda3 06401 0 0 00002 /dev/hda3 06402 0 0 [...all PV the same, PEs incrementing by one...] 00509 /dev/hda3 06909 0 0 00510 /dev/hda3 06910 0 0 00511 /dev/hda3 06911 0 0 00512 /dev/hdc3 06400 7 9 00513 /dev/hdc3 06401 0 0 00514 /dev/hdc3 06402 0 0 [...all PV the same, PEs incrementing by one...] 01021 /dev/hdc3 06909 0 0 01022 /dev/hdc3 06910 0 0 01023 /dev/hdc3 06911 0 0 _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
