Hittade denna guide som kan vara vettig om du ska sätta upp en ny RAID!
Jag blev förvånad över att "chunk size" skulle vara mindre om man skulle skicka stora filer och större när man skulle köra databas. Trodde det var tvärtom. Vettigt att läsa om du ska sätta upp en ny RAID på din server...
Chunk size: the hidden key to RAID performance
Stripes go across disk drives. But how big are the pieces of the stripe on each disk? The pieces a stripe is broken into are called chunks. Is the stripe broken into 1k byte pieces? Or 1 MB pieces? Or even larger? To get good performance you must have a reasonable chunk size.
So what is a reasonable chunk size? It depends on your average I/O request size. Here’s the rule of thumb: big I/Os = small chunks; small I/Os = big chunks.
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.
However, many databases use their own strategies to gather I/Os to minimize I/O overhead. In that case you need to know what the database is actually doing to choose the right chunk size.
Läs mer: Chunks: the hidden key to RAID performance | Storage Bits | ZDNet.com
