Raid 0 Question

S

Snow4832

Limp Gawd
Joined
Oct 31, 2002
Messages
141
If you have two 80gig harddrives wired with raid 0 they will be combined together to make 160 gig's right?
 
Well, after all the RAID overhead and such, it'll probably be something like 152 gigs.
 
Actually on a hardware raid controller there is no overhead in space. It uses each byte the same. The bandwidth will however not quite get to
double because of the overhead. Your access time will be larger too.
 
Well, since I have to WD 80GB hard drives hooked up in Raid 0, I can tell you I see 149GB according to Windows XP. :D That is with the built on Raid with a Gigabyte K8N Pro.
 
Yep, you're correct. It shows as 149MB because of windows' conversion from bits to bytes, blah blah blah. You can eat that space up pretty fast though depending on your cluster size. I'd be curious to know what most people are setting their cluster sizes at on their RAID arrays. I use to have one a few years ago using a hpt370 controller w/ 64KB clusters.
 
I have a current array with my Raptors in RAID0. I think mine is set to 64k clusters, but I'm wondering if I should have mine set to something different.
 
Originally posted by djnes
I have a current array with my Raptors in RAID0. I think mine is set to 64k clusters, but I'm wondering if I should have mine set to something different.
Click to expand...

64K was pretty standard when I had my array, but I swear I read something on [H]ard|OCP about 16K clusters being standard (I think the sys building guide), which is why I asked the question.

Even though 16K would waste less space, I think the "speed freaks" would rather lose a little more space to gain performance.:confused:
 
Ok you guys are talking about stripe size. Which does not really affect wasting space, but affects the performance of the RAID. Cluster size affect how much wasted space happens. These are two independent settings. stripe is set by the raid controller, cluster size is defined by the filesystem.
 
I'm not going to be sarcastic, i just want to understand how it works-

NTFS and FAT32 both use a 4K cluster size on disks larger than 2GB...which is determined by the OS, as you say.

Regardless, if a RAID array stripes a 96K file to the drive, then your saying that the remaining 32K between the two clusters is not wasted space?
 
According to MS, FAT32 has the following cluster sizes:

Code: 
   Partition size           Cluster size
   -------------------------------------
   512 MB to 8,191 MB          4 KB
   8,192 MB to 16,383 MB       8 KB
   16,384 MB to 32,767 MB     16 KB
   Larger than 32,768 MB      32 KB

The default cluster size in NTFS can be as small as 512 bytes. NTFS5 lets you use 512 byte clusters in larger partitions than NTFS4. In Windows when you format the drive (disk management or format /a:<size>), you can set the default cluster size. Or if using convert.exe to convert a FAT/FAT32 drive to NTFS, the default cluster size is 512 bytes.

To answer your question, the stripe size matters for performance purposes, but only cluster size determines the amount of wasted space. On average, 1/2 of last cluster in a file is "wasted", so wasted space can be determined as: <number of files on the hard drive> x 0.5 x cluster size. The amount of "wasted" space is almost negligible on a hard drive filled solely with very large files, but is pretty important on a hard drive with many small files.

16 clusters may fit in a 64KB stripe (FAT32 example for an under 8GB partition with 4KB clusters). Writing to 1 cluster in a stripe does not waste the other 15 clusters in this example. However, if only 1 cluster needs to be read/written in a stripe, the computer is wasting time moving data that it doesn't need to.
 
The smaller the clustet size the more effiecient howerver the larger the more perrformance you get. 64 k is the norm.

Intell on board controllers tell you 128 for perforamnce but be careful. I had an issue attemping a 128kb stripe on two 7k250 drives. Xp would not finish install and boot .

I went nuts trying every thing until i decided to go 64kb on the stripe and things went perfect. I cant explain it.

Any way they say 16kb is best for gaming but your boot times iwll suffer do to the high efficiency of the stripe. I recomned 64kb thats what i use and the performance is where i want it.
 
Originally posted by Iconz1
blah blah blah.
Click to expand...

I would assume blah blah blah = the additional space lost to the filesystem overhead :p
This overhead is in the from of NTFS system files and the log file, which can use several percent of the total disk space of a small volume
Click to expand...
(see the Advanced HDD Issues sticky thread > Alternative Filesystems
for more comparitive filesystem info)


Cluster size (and what determines it by default) where very well addressed :D

a bit more on stripe size
http://www.storagereview.com/guide2000/ref/hdd/perf/raid/concepts/perfStripe.html
http://www.systemlogic.net/articles/01/1/raid/page5.php

and
Binary vs Decimal Measurements
 
Originally posted by jacuzz1
Any way they say 16kb is best for gaming but your boot times iwll suffer do to the high efficiency of the stripe. I recomned 64kb thats what i use and the performance is where i want it.
Click to expand...

I just setup a RAID 0 array using two WD 80GB drives with 8MB cache. I'm using 64K clusters and all is fine until I run UT2K4. It crashed on both attempts to play it. First time on the ingame server browser and the second time it happened about 5 minutes into playing. Would you recommend decreasing the cluster size to 16K? I'm new to RAID so i'm not exactly sure how to fix this problem.
 
You must log in or register to reply here.
Back
Top