On Wed, 3 Apr 2002 00:29, Alvin Oga wrote: > > Chunk size does not matter for RAID-1, but does matter for other RAID > > levels. > > humm ..thought was the otehr way ... time for me to go look at some > raid source code i suppose .. when time permits
The chunk size determines physical location of the data for RAID-0 and RAID-5. For RAID-1 both disks will have exactly the same data, which is the same as what you would have if you only had one disk. So chunk size is not an issue. > > > if your disk was partitioned as... 2K bytes/inode... > > > > You probably mean 2K blocks. The number of bytes per inode just > > determines the size of the inode tables. > > yuppers ... and a block is 512bytes ( aka a sector ) No. A block is the allocation unit for the file system. For ext2 that can be 1, 2, or 4K (but generally no-one uses 2K). For ReiserFS it's always 4K. Other file systems have different options. > > If you have lots of little files then if you want good write performance > > then you want RAID-1 or RAID-10. RAID-5 is the cheap alternative. > > hummm ..... thinking outloud.... > > "cheap" is relative??? > - $$$ for disks vs "(usable) disk space lost to raid" Cheap is when you cut corners to save money. > typically a minimum of 2 disks used for raid0 or raid1... > raid1(mirroring) protects against one disk failure > ( one disk's capacity is used as a redundant copy and not for user) > ( 50% lost of space ) > > raid0(stripping) does not help for disk failures Yes. Also RAID-0 increases the probability of data loss unless you take other protective measures. If during a particular time period the probability of one disk failing is 0.1, then the probability of a RAID-0 failing is 1-(1-0.1)*(1-0.1) = 0.19. > typically 5 disks for raid5 ... > ( 3 disks mininum -- 1/3 of your disks lost to parity > ( 4 disks .......... 1/4 of your disks lost to parity > ( 5 disks .......... 1/5 of your disks lost to parity Another thing, you should have a separate cable for each disk you want to be independant. So for RAID-1 you should have two cables so that a cable failure won't lose your data. For a RAID-5 with 5 disks you want 5 cables. One setup I've seen had 30 disks with 5 RAID-5 arrays. There were 6 cables, each RAID-5 array had 5 data disks and one spare disk on separate cables. -- If you send email to me or to a mailing list that I use which has >4 lines of legalistic junk at the end then you are specifically authorizing me to do whatever I wish with the message and all other messages from your domain, by posting the message you agree that your long legalistic sig is void. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
