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Old 1st July 2011, 03:21 PM
seabird Offline
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Join Date: Jan 2009
Location: Den Bosch, Netherlands
Posts: 282
RAID chucnk size

Hi everyone,

just reading loads of articles before setting up my server again for F15 ....

I always thought:

large files --> big chunk size
small files --> small chunk size

Since my server is mostly movies, photo's, music I used to have a larger chunk size. Reading this article made me wonder if this was correct:
Do you do video editing or a lot of Photoshop work? Then your average request size will be large and your performance will be dominated by how long it takes to get the data to or from the disks. So you want a lot of bandwidth to move data quickly. To get a lot of bandwidth you want each disk to shoulder part of the load, so you want a small chunk size. What is small? Anywhere from 512 bytes (one block) to 8 KB.

If you are running a database and doing lots of small I/Os - 512 bytes to 4 KB say - then you want to maximize your IOPS, which ideally means sending each I/O to only one disk and spreading the I/Os evenly across the disks. What you don’t want is a single I/O getting sent to two disks, since waiting for the heads will slow things down. So you want a large chunk size - at least 64 KB or more. That large chunk will mean that most I/Os get serviced by a single disk and more I/Os are available on the remaining disks.
Any thoughts or feedback is welcome. I mainly run it as a samba share to directly edit files on the server.
OS: Fedora 16
Casing: Chenbro RM21508B
Mainboard: ATX D2778
Processor: Intel Xeon W3550 (8 core)
Memory: 6Gb DDR3, ECC, 1333 MHz, PC3-10600
HD #1: OCZ Vertex 3 60Gb
Storage Drives: 4x 2Tb WD20EARS + 2x 2Tb WD20EARX
Graphics: Nvidia GeForce 210 Silent
PCI Card: Promise FastTrak TX4
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chucnk, raid, size

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