[CentOS] Re: RAID Hot Spare
on 2/1/2008 3:57 PM Dean Maluski spake the following: I've googled this question without a great deal of information. Monday I'm rebuilding a Linux server at work. Instead of purchasing 3 drives for this system I purchased 4 with intent to create a hot spare. Here is my usual setup which I'll do again but with a hot spare for each partion. Create /dev/md0 mount point /boot RAID1 3 drives with 1 hot spare Create two more raid setups /dev/md1 mount point / RAID5 3 drives with 1 hot spare /dev/md2 mount point /home RAID5 3 drives with 1 hot spare Now do I create partions of equal size for each set then if I remember correctly when creation the RAID there is a check box for hot spare. Do I just marry the 3 equal partions, click the check box and assume the system will find the partition of equal size and use it when needed? Makes no sense to me. Of couse will be creating RAID0 swap but leaving that out of the question for obvious reasons. Your raid0 swap will be a weak link if your system is swapping when the drive dies. -- MailScanner is like deodorant... You hope everybody uses it, and you notice quickly if they don't signature.asc Description: OpenPGP digital signature ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
[CentOS] Re: RAID Hot Spare
on 2/1/2008 4:33 PM Dean Maluski spake the following: On Fri, 2008-02-01 at 16:11 -0800, nate wrote: Dean Maluski wrote: I've googled this question without a great deal of information. Of couse will be creating RAID0 swap but leaving that out of the question for obvious reasons. You really should use anything but RAID 0 for swap. If you need to swap and that device is dead then your system is hosed. At one point I read that you can get RAID0-"like" performance by having multiple swap partitions on multiple devices and mounting them with the same priority(mount option pri=(some number)). It (was/is) supposed to stripe the swap partitions. Not sure if that ever worked, though I have configured systems over the years to use matching swap priorities, never really looked to see if it was doing what I expected though. Yeah, from swapon(2): [..] If two or more areas have the same priority, and it is the high-est priority available, pages are allocated on a round-robin basis between them. nate OK, not really an answer to my hot spare question. What I read sounds similar to what you state that if you create multiple swap partions the system will create a raid0 of it. So what is the recommendation? create 1 swap partition on one drive? And for your hot spare question, you create the raid arrays the normal way, with raid type, number of drives set to 3, set the number of spares to 1, and have the 4 partitions on the command line. mdadm --create --level=5 --raid-devices=3 --spare-devices=1 /dev/part1 /dev/part2 /dev/part3 /dev/part4 It is all in the man page if you want other options. -- MailScanner is like deodorant... You hope everybody uses it, and you notice quickly if they don't signature.asc Description: OpenPGP digital signature ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
[CentOS] Re: RAID Hot Spare
on 2/1/2008 4:33 PM Dean Maluski spake the following: On Fri, 2008-02-01 at 16:11 -0800, nate wrote: Dean Maluski wrote: I've googled this question without a great deal of information. Of couse will be creating RAID0 swap but leaving that out of the question for obvious reasons. You really should use anything but RAID 0 for swap. If you need to swap and that device is dead then your system is hosed. At one point I read that you can get RAID0-"like" performance by having multiple swap partitions on multiple devices and mounting them with the same priority(mount option pri=(some number)). It (was/is) supposed to stripe the swap partitions. Not sure if that ever worked, though I have configured systems over the years to use matching swap priorities, never really looked to see if it was doing what I expected though. Yeah, from swapon(2): [..] If two or more areas have the same priority, and it is the high-est priority available, pages are allocated on a round-robin basis between them. nate OK, not really an answer to my hot spare question. What I read sounds similar to what you state that if you create multiple swap partions the system will create a raid0 of it. So what is the recommendation? create 1 swap partition on one drive? It depends. If you are going to create LVM over the large raid5 partition you could put the swap there. Or you could create a raid 1 the same way you create the /boot partition. If the system is properly sized, swap is less of a performance issue anyway. -- MailScanner is like deodorant... You hope everybody uses it, and you notice quickly if they don't signature.asc Description: OpenPGP digital signature ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
