From: Ming Z. <mi...@el...> - 2005-07-27 17:13:00
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On Thu, 2005-07-28 at 01:01 +0800, Feizhou wrote: > >>>>unless you have free hotswap SCSI bays available, adding another > >>>>software raid will have to mean another box with iet. > >>>> > >>>> > >>>> > >>>> > >>>but raid5 can not dynamic add disk and expand size right? > >>> > >>> > >>> > >>> > >>> > >>no, hence the need for lvm...but at the same time, lvm does not tolerate > >>disk loss. > >> > >> > >so that is why i am thinking lvm on top of several raid5 or 1 > > > > > > > where the raid5/1 is composed of devices that are available through iscsi. > u are talking about distributed iscsi raid. complex enough, my head ran slower now. > >>> > >>> > >>> > >>> > >>>>At same blinking time, lvm does not tolerate losing physical volumes so > >>>>if a iet box goes down.... > >>>> > >>>> > >>>> > >>>> > >>>iet is on top of lv, so even iet box crash, hopefully lvm is still > >>>there. > >>> > >>> > >>> > >>> > >>> > >>you still need lvm on the database box itself to do dynamic resizing. > >> > >> > >why? i resize the lv iet exports and then ini side see new size scsi > >disk. > > > > > > > > > this does not work. you cannot just resize a device. this will drive the > kernel/filesystem on the initiator side nuts. > linux might not support this. but in scsi spec, u 100% can resize a LUN and report to initiator. > >>> > >>> > >>> > >>> > >>>>very murky this one > >>>> > >>>> > >>>> > >>>> > >>>:P any suggestion? > >>> > >>> > >>> > >>> > >>i had a hard think on this one...linux lvm don't do fault tolerance but > >>md does...so where do you use these pieces on the initiator box and or > >>the target box and how to combine them is a bit sketchy at the moment. > >> > >> > >we need a complete solution... > > > > > > > > > which comes down to multiple iet boxes. iet locally raided for > redundancy. then the initiator box will have to use raid on multiple iet > exported devices and treat those as a PV for the initiator LVM. Adding > to the VG will mean adding a set of iet boxes. higher cost. :P if i want a raid5, that means i at least need 3 iet box and the more iscsi disk i want to have, the more boxes i wasted. and also since raid can not resize, add a vg, as u said, i need another SET of iet box. not 1 or 2. a SET. :P ming |