On Sunday 13 June 2004 10:21, Shachar Shemesh wrote: > Erez Boym wrote: > >Hi, > > > >I'm planning on building a home server and planning to > >add RAID to that server for both seamless large HD and > >backup I have stumbled across a small RAID question: > > > >I'm planning on 4x200G HDDs and I want to set them in > >such a way that I will have 2 fully mirrored 400G > >HDDs. Hence to take HD 1 and 2 and create a large 400G > >out of them, then take HD 3 and 4 and create a large > >400G out of them, then have the HD3&4 as a full mirror > >of HD1&2. > > > >Is that possible? > > > >What type or RAID do I need (0,1,2 .....) ? > > > >Thanks > > > >Erez > > What you are describing boils down to having either stripping or raid-0 > between disks 1 and 2, and 3 and 4. Then you will have raid-1 between > the first and the second disks. what some people call raid 10. which is raid 0+1 - a mirror on a stripe (or a stripe on a mirror). This type of an array is common when dealing with mission critical machines, this, or just plain mirroring (raid 1). > > However, please consider the following: > 1. You did not say what bus your hard-disks are using. If they are IDE, > placing two hard disks in raid over the same IDE bus will yield > performance penalty. The only practical way to connect four IDE > hard-disks in raid is to add two more IDE buses to the two that come > standard. why would anyone want to do IDE raid anyway? - if youre going for 4 hds or more, i'd suggest SCSI. > 2. If you are going to have 4x200G, why not do one Raid-5 (resulting in > 600G useable space), rather than 2xRAID-0+RAID1 (resulting in 400G)? i would suggest that too - with your IDE controller youre going to have quite a big penalty on performance, so just go for raid 5 - you also get the redundancy you want, and also an extra 200gb. i cant comment too much on raid 5 with software, but from my experience, if youre going for raid 5, you better have a raid controller (like, do it on hardware). > 3. The difference between RAID-0 and stripping is worth reading. If you > are going to be locked in to the current disk sizes, then RAID-0 is > probably better for you. If there is a chance that you will add more > disks, use stripping. raid 0 is what we call striping, but you probably meant raid 1. about the extensibility of arrays - if were using striping (raid 0), then the only way most common controllers, or volume managers allow you to extend your array is by adding another stripe set, in your case erez, it is only if you buy an extra 4 hd's in the same size (notice they _do not_ have to be in the same size of the previous 4). raid rebuilds usually cause headaches and are not worth it. if youre going to extend your array, then use just linear raid, which gives you the opputunity to extend your array, but then you have no redundancy. > > Shachar
A couple of more points : Raid 1 - mirroring - you get a boost in reading, because you have 2 heads reading the same data. Raid 0 - striping - you get the boost in writing - you can understand why. Raid 4/5 - striping with checksum - you get some boost in writing, but then you have a penalty calculating your checksum. All in all, i'd just suggest you to do raid 5, take the penalty, and if you dont have the extra money for a controller - do it with software. Enjoy, Dan. ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
