Hi Mark, I'm currently running a 4 disk RAID 5 on a 3Ware 6800 card under mdk 8.2. The card uses a combination of hardware, firmware, and software to operate so it is not a 'true' hardware RAID, but it still works pretty good for many situations. Here are the pros and cons that I have come across with this solution concerning RAID 5 arrays:
Pros: 1. mdk 8.0 and up will recognize the card and will view the an array as one disk from the get go. (The last time that I messed with software raid, the mdk installer didn't handle software raid so you had to set it up after installation.) 2. Fast reads with current drivers. 3. Good array monitoring software. 4. Lastest firmware drivers handle 48-bit addressing. 5. Handles single drive failures and power loss quite well from personal experience. Cons: 1. Slow writes. (Tops out around ~5 MB/s for me.) They made an improvement so that large writes go a lot faster than it used to. The problem is that the card has a very small onboard memory so it just cannot efficiently do RAID 5 writes. (Relies on harddrive caches which is supposed to work well in RAID 0 and RAID 1.) The 7x50 series are supposed to have an extra cache chip to dramatically speed up RAID 5 writes. ----- With my experience with purely software RAID under Linux, each disk in the array is labled, so if you even pull the disks out and stick them in a different order, Linux will still figure out which drive is which. All of the RAID configuration can be figured out automatically from information stored on partition, so yes you should be able to yank the disks from one machine and stick them into another. > I want to install a RAID on my server, currently running Mandrake 8.2, in > order to improve data integrity and guard against hardware failure. I've > downloaded raidtools-0.9 rpm and installed it, the next things is to buy > the hardware. I'm not sure whether to run RAID 1 or RAID 5, presumably I'll > need two disks for the former and three for the latter? But do all the > disks need to be identical? > > What happens if I have a major system problem and need to recover data from > another machine? If I use RAID 1 I can restore from either disk on a > machine without raidtools but with RAID 5 I'd need any two of the disks > plus a machine with raidtools installed, is this correct? > > What other implications should I be aware of when using software RAID? > > Any help/experiences much appreciated. > > Thanks, > > Mark
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