Hi,
I am working with a research group that is currently building a tool to automatically find bugs in file systems, and related questions. We are trying to check whether file systems really guarantee the consistencies they promise, and one aspect we are looking at is running them on top of Raid devices. In order to do this we have to understand a few things about the Linux Raid driver/tools and I haven't been able to figure this out from the documention/source code, so maybe you can help me.
I asked this same question a few days ago, but I think I didn't really state it clearly, so let me try to rephrase it.
For Raid 4-6 and for say 5 disks say we write a block that is striped across all the disks, and after 4 of the disks write their part of the block to disk the machine crashes without the 5th disk being able to complete the write. Because of this, the checksum for this stripe should be incorrect, right?
The raid array is a Linux soft raid array set up using mdadm, and none of the disks actually crashed or wrote had any errors during this operation (the machine crashed for some other reason) We then reboot the machine and recreate the array, then remount it and then try to read the sector that was previously written (that has an incorrect checksum). At what point will the raid driver discover that something is wrong? Will it ever (I feel that it should discover this during the read at latest). Will it try to perform any kind of recovery or simply fail?
How would this change if only 3 of the 5 disk writes made it to disk? Fixing the error would be impossible of course (at least with Raid 4 and 5, i know little about 6), but detection should still work. Will the driver complain?
Thank you so very much for your help, Can
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