FR1 2.15b reviewDownload
FR1 is a Linux kernel driver that adapts the kernel's own software RAID1 driver. It's intelligent in that it doesn't blindly resyn
FR1 is a Linux kernel driver that adapts the kernel's own software RAID1 driver.
It's intelligent in that it doesn't blindly resynchronize a whole mirror component when only a few blocks need resyncing. That can save hours of resync time on a large device. In addition, it always chooses the fastest device to read from on reads.
The driver keeps a bitmap of pending writes in memory, and writes them to the mirror component that's just been repaired when it comes back on line. The bitmap is two-level and created pagewise on demand, so it's not too expensive.
A terabyte sized device with blocks of 4K will cost max 32MB of memory per mirror component, thus 64MB max for a two component mirror.
But in practice only a few pages of bitmap will have been allocated by the time you come to fix the device.
Ditto for arrays with spare components. The 2.4 kernel code is very obscure in the area of array management and I can be excused! The situation has bettered in 2.6, but it is still not perfectly obvious code.
I really don't know what to do about mirror components that have a nonzero offset recorded for them in the array metadata. I've never seen it in the field. Probably things will go horribly wrong.
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