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.)
That's my understanding, RAID1 is more wasteful though (you loose 1/2 of your storage).
- 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.
To use software RAID comes down to expected load on the computer (i.e. do you have spare CPU power to use on it).
I haven't setup a hardware RAID, but my understanding of it is that as it is done by hardware the software (i.e. Linux) doesn't know or care if it is a RAID system it just uses it as if it is an ordinary drive.
- 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?
Most of these are a software raid implemented in the BOIS, and from my reading not recommended to be used, mdadm is much more sophisticated.
- The 3ware 9550SX looks good, and there's even a Sarge install: http://www.3ware.com/KB/article.aspx?id=14860Has 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
I am using a software RAID with 4 drives, 2 PATA drives and 2 SATA drives, all 200GB, all partitioned with 3 partitions, 1 small, 1 medium, 1 large.
The PATA drive are each on a separate controller, so if on of those fail it can't stop the other PATA drive, which is possible if both where on the same cable.
I used a software raid1 over 2 small partitions of the drives for the /boot partition, as my Linux can only boot from a RAID1 partition, and used the other two small partitions as a parallel swap partitions.
I used a software raid5 on all the medium partitions for the Linux install, and a software raid5 on the large partitions as a network wide storage.
This has worked fine for me.