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
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