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I have just bought the LSI MegaRAID SAS 8204ELP off eBay and have been looking at the specs of it. It says that it has support for >2TB logical drive. Now, forgive me if I'm stupid, but does this mean that any RAID array can be over 2TB or that it supports 2TB and above sized drives.

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The logical part would suggest that the drive you end up with can exceed 2TB, rather than supporting the actual use of 2TB drives.

I cannot find any documentation on their site regarding the support of 4KB sectors or >2TB drives, the date of the latest BIOS on their site could mean they do support the technologies, but there's no way to really tell without raising the question to their support people.


Some light reading on 4KB sectors that may affect the drives you buy:,2554.html

The key thing you need to know as a user is:

The Performance Trap

If 512 byte data has to be written across two physical 4KB blocks, the hard drive will have to read the 4KB blocks that are affected, introduce the modifications, and write them back onto the drive. This process is referred to as read-modify-write (RMW). While this doesn’t hurt much if it happens here and there, it becomes a significant issue if the alignment of eight 512 byte sectors into only one physical 4KB block is wrong. Therefore WD offers either its Alignment software (information and downloads can be found here), which rearranges all data on a hard drive to fit the logical 512 byte sectors into the physical 4KB sectors.

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OK thanks. I know there is a jumper that can be set to make it go back into a normal drive. Is there really any difference with the 4KB cluster? – Dean Perry Jan 21 '11 at 21:29
Sorry, I should have said "4Kb sectors" and not clusters. If the drive uses 4kb sectors, the controller is 4kb aware and passes that info on to the OS, then when the OS creates the drive it will align the partitions on a 4kb boundary and write the drive with 4kb sectors. If any of those don't happen then performance will degrade as then whenever a file is written that uses part (but not all) of a 4kb sector then the drive will have to read the existing data and then write out the new sector. The performance lost should only be at the beginning and end of long files that traverse sectors. – Mokubai Jan 21 '11 at 21:37
Learn more about 4kb – Moab Jan 22 '11 at 15:23

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