Messages in this thread | | | Date | Thu, 14 May 1998 11:14:40 -0400 | From | Pierre Phaneuf <> | Subject | Re: journaling filesystem |
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David Woodhouse wrote:
> > mechanism for write ordering. Assuming that either write-through > > caching is used or write-back with the battery backup unit, the > > controller will guarantee that once the OS has been told the write has > > completed successfully then the disks will be updated eventually > > unless enough of a hardware failure occurs. > > In that case we'll need a mechanism for detecting the battery backup unit, and > enabling write-through operation if it's absent. That should suffice.
This should be in userspace, à la hdparm. If the machine has a UPS, the admin possibly has a clue or two (of course, since he's running Linux in the first place!), so he'll tweak the machine accordingly, including setting up a powerd and putting some hdparm in the rc.local file.
> If we could provide the same kind of control on all devices (partial ordering, > complete cache flush, whatever) then a single strategy could be used to ensure > consistency on each type of device. Otherwise we might have to implement > slightly different filesystem routines, depending on the type of device it's > on. We may well want to do things slightly differently, depending on the > facilities available from the block device.
There should be just a simple "sync()" function for block devices (if there isn't already one) implemented, so that you simply sync() the journal device after writing to it. I think this would be very general and could be used in other contexts. Other way would having "really raw" block devices... I think database people are asking for this?
-- Pierre Phaneuf Web: http://newsfeed.sx.nec.com/~ynecpip/ finger: ynecpip@newsfeed.sx.nec.com
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