2011/5/3 Morad, Steve [off-list ref]:

I have a few questions about volume mirroring performance implications.

1. I'm looking for an optimal configuration to maximize read speed while protecting the data from a disk failure (e.g. for an application that primarily does reads).  For RAID 1, does the linux raid driver perform parallel read requests across all available disks?  If, for example, I set up a RAID 1 volume with 4 disks, would the OS handle concurrently reading (different) data from all 4 disks at the same time?

today read_balance algorithm is optimized for multi-thread
read algorithm preffer disk with minimal head distance (current block
- block that will be read)

you can unselect disks setting they as write-mostly

optimizations at raid1 aren´t for bigger sequencial read, they are for
multi-thread

2. Similarly, would a RAID10 configuration give me the same (or better) read behavior across these same disks, while providing twice the storage capacity of the above configuration?

in md world
raid1+ raid0 != raid10

raid10 can use layouts
raid1 can´t

raid10 have diferent read_balance algorithms than raid1
raid10 with far layout is better optimized for sequencial read (it´s
like raid0 stripe)
raid10 with near/offset layoute are better optimized for multthread

3. Is the raid driver smart enough to keep track of underlying volume performance history or queue lengths and make read requests appropriately? For example, if for some crazy reason a 10K disk was mirrored with a 7K disk, would the OS make more read requests to the 10K disk than to the 7K disk, or would read requests be equally distributed across both disks?

no
i made a new raid1.c algorithm for kernel 2.6.37, that you can change
this options, you will have 1% of speed improvement in a very high
workload of read (ok it´s not a lot but i tested three times (1 hour
non sequencial test) and 1% are seeing, it´s not a error of
benchmark), you can mix SSD and HD too

code is here:
http://www.spadim.com.br/raid1/


it´s not a md-team solution
it´s a patch, more information inside the file
to compile you must compile like anyother kernel module
make drivers/md/raid1 ....

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Roberto Spadim
Spadim Technology / SPAEmpresarial
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