Re: [CentOS] Software RAID10 - which two disks can fail?
On Tuesday, April 08, 2014 03:47 AM, Rafał Radecki wrote: As far as I know raid10 is ~ a raid0 built on top of two raid1 ( http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_1.2B0 - raid10). So I think that by default in my case: No, Linux md raid10 is NOT a nested raid setup where you build a raid0 on top of two raid1 arrays. /dev/sda6 and /dev/sdb6 form the first raid1 /dev/sdd6 and /dev/sdc6 form the second raid1 So is it so that if I fail/remove for example: - /dev/sdb6 and /dev/sdc6 (different raid1's) - the raid10 will be usable/data will be ok? - /dev/sda6 and /dev/sdb6 (the same raid1) - the raid10 will be not usable/data will be lost? The man page for md which has a section on RAID10 describes the possibility of something is absolutely impossibe with a nested raid1+0 setup. Excerpt: If, for example, an array is created with 5 devices and 2 replicas, then space equivalent to 2.5 of the devices will be available, and every block will be stored on two different devices. So contrary to this statement: RAID10 provides a combination of RAID1 and RAID0, and is sometimes known as RAID1+0., linux md raid10 is NOT raid1+0. Is something entirely new and different but unfortunately called raid10 perhaps due to it being able to create a raid1+0 array and a different layout using similar concepts. I read in context of raid10 about replicas of data (2 by default) and the data layout (near/far/offset). I see in the output of mdadm -D the line Layout : near=2, far=1 and am not sure which layout is exactly used and how it influences data layout/distribution in my case :| I would really appreciate a definite answer which partitions I can remove and which I cannot remove at the same time because I need to perform some disk maintenance tasks on this raid10 array. Thanks for all help! If you want something that you can be sure about, do what I do. Make two raid1 md devices and then use them to make a raid0 device. raid10 is something cooked up by Neil Brown and but is not raid1+0. http://en.wikipedia.org/wiki/Linux_MD_RAID_10#LINUX-MD-RAID-10 ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Software RAID10 - which two disks can fail?
The raid10 name is very misleading. I came to the same conclusion yesterday: for sake of clarity I will make two raid1 arrays and combine them into a raid0 ;) Thanks for all info. BR, Rafal. 2014-04-08 8:49 GMT+02:00 Christopher Chan christopher.c...@bradbury.edu.hk : On Tuesday, April 08, 2014 03:47 AM, Rafał Radecki wrote: As far as I know raid10 is ~ a raid0 built on top of two raid1 ( http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_1.2B0 - raid10). So I think that by default in my case: No, Linux md raid10 is NOT a nested raid setup where you build a raid0 on top of two raid1 arrays. /dev/sda6 and /dev/sdb6 form the first raid1 /dev/sdd6 and /dev/sdc6 form the second raid1 So is it so that if I fail/remove for example: - /dev/sdb6 and /dev/sdc6 (different raid1's) - the raid10 will be usable/data will be ok? - /dev/sda6 and /dev/sdb6 (the same raid1) - the raid10 will be not usable/data will be lost? The man page for md which has a section on RAID10 describes the possibility of something is absolutely impossibe with a nested raid1+0 setup. Excerpt: If, for example, an array is created with 5 devices and 2 replicas, then space equivalent to 2.5 of the devices will be available, and every block will be stored on two different devices. So contrary to this statement: RAID10 provides a combination of RAID1 and RAID0, and is sometimes known as RAID1+0., linux md raid10 is NOT raid1+0. Is something entirely new and different but unfortunately called raid10 perhaps due to it being able to create a raid1+0 array and a different layout using similar concepts. I read in context of raid10 about replicas of data (2 by default) and the data layout (near/far/offset). I see in the output of mdadm -D the line Layout : near=2, far=1 and am not sure which layout is exactly used and how it influences data layout/distribution in my case :| I would really appreciate a definite answer which partitions I can remove and which I cannot remove at the same time because I need to perform some disk maintenance tasks on this raid10 array. Thanks for all help! If you want something that you can be sure about, do what I do. Make two raid1 md devices and then use them to make a raid0 device. raid10 is something cooked up by Neil Brown and but is not raid1+0. http://en.wikipedia.org/wiki/Linux_MD_RAID_10#LINUX-MD-RAID-10 ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Software RAID10 - which two disks can fail?
On 4/8/2014 12:35 AM, Rafał Radecki wrote: The raid10 name is very misleading. I came to the same conclusion yesterday: for sake of clarity I will make two raid1 arrays and combine them into a raid0;) Thanks for all info. its striped mirrors, its just that it treats it all as one big raid rather than as distinct subraids. having the separate mirrors and stripe can be an annoying complication, Ive done it that way plenty of times before. /dev/md2: /dev/md0: /dev/sda1 /dev/sdb1 /dev/md1: /dev/sdc1 /dev/sdd1 meh. ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
[CentOS] Software RAID10 - which two disks can fail?
Hi All. I have a server which uses RAID10 made of 4 partitions for / and boots from it. It looks like so: mdadm -D /dev/md1 /dev/md1: Version : 00.90 Creation Time : Mon Apr 27 09:25:05 2009 Raid Level : raid10 Array Size : 973827968 (928.71 GiB 997.20 GB) Used Dev Size : 486913984 (464.36 GiB 498.60 GB) Raid Devices : 4 Total Devices : 4 Preferred Minor : 1 Persistence : Superblock is persistent Update Time : Mon Apr 7 21:26:29 2014 State : clean Active Devices : 4 Working Devices : 4 Failed Devices : 0 Spare Devices : 0 Layout : near=2, far=1 Chunk Size : 64K UUID : 1403e5aa:3152b3f8:086582aa:c95c4fc7 Events : 0.38695092 Number Major Minor RaidDevice State 0 860 active sync /dev/sda6 1 8 221 active sync /dev/sdb6 2 8 542 active sync /dev/sdd6 3 8 383 active sync /dev/sdc6 As far as I know raid10 is ~ a raid0 built on top of two raid1 ( http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_1.2B0 - raid10). So I think that by default in my case: /dev/sda6 and /dev/sdb6 form the first raid1 /dev/sdd6 and /dev/sdc6 form the second raid1 So is it so that if I fail/remove for example: - /dev/sdb6 and /dev/sdc6 (different raid1's) - the raid10 will be usable/data will be ok? - /dev/sda6 and /dev/sdb6 (the same raid1) - the raid10 will be not usable/data will be lost? I read in context of raid10 about replicas of data (2 by default) and the data layout (near/far/offset). I see in the output of mdadm -D the line Layout : near=2, far=1 and am not sure which layout is exactly used and how it influences data layout/distribution in my case :| I would really appreciate a definite answer which partitions I can remove and which I cannot remove at the same time because I need to perform some disk maintenance tasks on this raid10 array. Thanks for all help! BR, Rafal. ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Software RAID10 - which two disks can fail?
On 4/7/2014 12:47 PM, Rafał Radecki wrote: As far as I know raid10 is ~ a raid0 built on top of two raid1 ( http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_1.2B0 - raid10). So I think that by default in my case: /dev/sda6 and /dev/sdb6 form the first raid1 /dev/sdd6 and /dev/sdc6 form the second raid1 So is it so that if I fail/remove for example: - /dev/sdb6 and /dev/sdc6 (different raid1's) - the raid10 will be usable/data will be ok? - /dev/sda6 and /dev/sdb6 (the same raid1) - the raid10 will be not usable/data will be lost? I'm not sure you can verify that I would play it safe, and only drop one drive at a time. -- john r pierce 37N 122W somewhere on the middle of the left coast ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Software RAID10 - which two disks can fail?
On 2014-04-07, Rafa? Radecki radecki.ra...@gmail.com wrote: I would really appreciate a definite answer which partitions I can remove and which I cannot remove at the same time because I need to perform some disk maintenance tasks on this raid10 array. Thanks for all help! You're likely to get the most definitive answer from the linux RAID mailing list. http://vger.kernel.org/vger-lists.html#linux-raid Many of the md developers hang out there, and should know the correct answer. (I'm afraid I don't know it myself.) --keith -- kkel...@wombat.san-francisco.ca.us ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
