[PATCH/RFC] Linux MTD striping middle layer
Artem B. Bityutskiy
dedekind at infradead.org
Tue Mar 21 10:09:24 EST 2006
I have basic questions as I haven't grasped your concepts. Note, I'm not
an expert in RAID, so please, bother to explain basic notions as well.
Belyakov, Alexander wrote:
> In the suggested solution it is possible to stripe 2, 4, 8, etc.
> of the same type. Note that devices with different sizes are
Why can't I have 3 or 5 chips and enable striping?
> <stripedef> :=
> insmod mtdstripe.ko
> Note: you should use '.' as a delimiter for subdevice names here.
Err, please, define the "subdevice" notion. And what is vol1, vol2, etc?
Please, describe the model of the striped MTD device from user's
perspective. I understand MTD concatenation. It just merges several MTD
devices to one larger MTD device.
May I consider your striping as another type of MTD concatenation layer
which concatenates MTD devices by means of interleaving eraseblocks?
> Subdevices should belong to different (independent) physical flash
> chips in order to get performance increase. Value "interlavelsize"
> describes striping granularity and it is very important from
> point of view. Write operation performance increase should be expected
> only if the amount of data to be written larger than interleave size.
> For example, if we have 512 bytes interleave size, we see no write
> boost for files smaller than 512 bytes. File systems have a write
> well known size (let it be 4096 bytes). Thus it is not good idea to
> interleave size larger than 2048 byte if we are striping two flash
> and going to use the file system on it. For NOR devices the bottom
> for interleave size is defined by flash buffer size (64 bytes, 128
> bytes, etc).
Err, what does interleaving in sizes non-multiple to the eraseblock size
mean. Suppose my interleave value is 512. Suppose the interleaved MTD
device name is mtd7 and it concatenates 2 other MTD devices. What
1. I write 512 bytes at offset 0 of eraseblock 0 of mtd7
2. I write 512 bytes at offset 512 of eraseblock 0 of mtd7
3. I write 512 bytes at offset 1024 of eraseblock 0 of mtd7
4. I erase eraseblock 0 of mtd7
Artem B. Bityuckiy,
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