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4 Tellurium

## how many data would be replied in this case??

Hi all,

Suppose we have a [4+1 RAID-5] LUN, the strip size = 64kb(128 sectors), so the entire stripe for this RAID-5 LUN is 64*4 =256KB(doesn't account parity drive).

Now one 4KB read I/O comes to this LUN, my question is: how many data will be replied? A full strip (64KB) or just 4KB successive data within one strip (don't account for disk crossing)?

thanks!

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5 Tungsten

## Re: how many data would be replied in this case??

It should just pull the 4KB from the LUN. I believe all data IO size is read from LUN as the size of the IO.

glen

4 Replies
5 Tungsten

## Re: how many data would be replied in this case??

The first 64KB that comes in (Write) will go to the first Element on the first disk. If the size is 4KB, it will still go into the first Element. For Intel-based OS, make use you have aligned the file system (not Windows 2008 - already aligned).

glen

4 Tellurium

## Re: how many data would be replied in this case??

Hi Glen,

Actually, i want to know the read scenario, not write. Is it just 4KB in this case? Then i would understand that one strip (element as terms of EMC) is not the smallest unit of one I/O operation.

thank you

5 Tungsten

## Re: how many data would be replied in this case??

It should just pull the 4KB from the LUN. I believe all data IO size is read from LUN as the size of the IO.

glen

4 Tellurium