Jason Snyder wrote: >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 >> > Umm, not quite. RAID4 and RAID5 will tolerate the loss of ONE drive out of the drives in the array of N drives and they both have a storage capacity of (N-1)*smallest drive (if you are using a hardware RAID) For software RAIDS they don't necessarily span disks and all sorts of mixtures are possible. RAID1 can also be set up with several drives and you can lose all but one.
Diskdrake does a wonderful job of setting up software RAIDs, And I have tested them with all 4 journaling filesystems in RAID0, 1, and 5 using a mix of IDE and SCSI drives without any RAID hardware. The downside is that the update function will absolutely not work with a RAID0 or RAID5 /. If / is RAID1 or just a plain partition, then no problem. I have run 8.0 with Mylex DAC960 controllers RAID0 and RAID5... You can find an article in forum about it, using 8.0 with kernel 2.2 and the old kernel 2.2 reiser. RAID is a lot easier than most folks think. RAID0 can improve performance dramatically with the right chunksize and perhaps 2 or 3 disks in the striping. Software RAID runs well, so you do not need identcal disks. Hardware RAID runs well and will base its work on the SMALLEST disk ikn the array if they are not identical. RAID1 requires two disks, RAID4 or RAID 5 requires 3 or more, and a system with a 5-disk RAID5 will store 4 times the smallest disk. RAID5 is not transferrable to a non-RAID machine, but with clever configuration of software RAID, that would not be an insurmountable problem. RAID1 will transfer with no problems, if it is a hardware RAID. IDE hardware RAIDs are rare. ARCO makes one, and Promise makes the SuperTrak. The ARCO is RAID1 only. For more info about what iIDE RAIDs are supported go to www.linux-ide.org/chipsets.html Civileme > > >------------------------------------------------------------------------ > >Want to buy your Pack or Services from MandrakeSoft? >Go to http://www.mandrakestore.com >
Want to buy your Pack or Services from MandrakeSoft? Go to http://www.mandrakestore.com
