I am partial to software raid for one important reason.... longevity. One great thing about linux is that it rarely makes something entirely obsolete... and even if it does, you can always download previous versions of your favorite distro... an array created by mdadm today will likely be readable by most linux distros for many years to come.
this is unlike hardware which can become almost impossible to replace in a few months sometimes. I've heard stories about hardware controllers that wouldn't read data from arrays created by previous versions of the same model controller due to an updated bios, and it was almost impossible to get the previous version from the manufacturer. As far as the best redundancy... I like raid 50. Raid 50 is essentially a raid 5 array that is mirrored to another raid 5 array... this protects from multi-drive failures as long as one of the raid 5 arrays only suffers a single drive failure... if both have multiple failures you may be able to recover if you can swap drives to build one array with one or zero failed disks. Of course, raid 50 is very wasteful... as not only do you waste 50% capacity for the mirror, but also 1/n% (n is number of drives in each raid 5 array) for the parity. Essentially, an array equivalent to the capacity of 2 disks would require 6 disks in raid 50 configuration. As far as performance... yes, a true respectable hardware controller will outperform software while also reducing the CPU load, This will make the machine much faster overall... for some things. If your building a file server for example... will it matter if the IO consumes more CPU cycles, and if your pulling data through a 100Mb link will the network be the bottleneck or the controller? This is all very dependant upon your needs... I have a couple of servers that are nothing but old workstations with PCI SATA controllers, 4 drives, and software raid that act as file servers for a few users... they tell me that they are faster than the Dell (w/ a PERCII SCSI HW RAID) that they were on before. Probably due to running a minimal installation of Debian instead of W2K. That's my 2 cents! Joe. On Friday 27 January 2006 2:57 pm, David Gaudine wrote: > I have to set up a system that is totally reliable w.r.t. data > integrity. That is, if a disk (or anything else) fails, it's OK if the > system is down for a few hours, but when it comes back up it has to be > exactly as it was, i.e. I can't restore from the previous day's backup. > The obvious solution is to use RAID level 1. Questions; > > - Is level 1 as reliable as level 5? My understanding is that level 5 > has better performance than level 1, but comparable reliability (maybe a > bit less, since disaster occurs if 2 out of 3 disks go bad at the same > time.) > > - I need to use RAID for everything, not just some partitions, so the > root has to use RAID. I've found lots of websites that describe doing > that with software (mdadm), but very little about hardware. Using > software is cheap and seems to be simple, but I assume hardware gives > better performance. Is the performance difference significant? If not, > I guess my further questions don't matter. But I'd rather spend money > than give up performance. > > - Many/most modern motherboards claim to support RAID. Are any of them > useful, or do they all just provide a BIOS that fakes it well enough for > Windows but not for Linux? > > - The 3ware 9550SX looks good, and there's even a Sarge install: > http://www.3ware.com/KB/article.aspx?id=14860 > Has anyone tried the installer? I can't unless I buy the card (and a > computer to put it in) first. I don't know whether it will do the whole > job of allowing me to properly set up everyting on RAID at installation > time, although that seems like the point of having it in an ISO instead > of just having a driver module. > > - Any other ideas about a RAID board that's supported by a Sarge install > or for which there are step-by-step instructions how now to install > Sarge and then move it to RAID as is frequently done for mdadm? > > David -- Joseph H. Fry Network Administrator School Of Architecture University of Detroit Mercy (313) 993-1507 [EMAIL PROTECTED] -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
