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 8 6 0 active sync /dev/sda6
1 8 22 1 active sync /dev/sdb6
2 8 54 2 active sync /dev/sdd6
3 8 38 3 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.
On 4/7/2014 12:47 PM, Rafa? 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
On 2014-04-07, Rafa? Radecki <radecki.rafal at 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 -- kkeller at wombat.san-francisco.ca.us
Christopher Chan
2014-Apr-08 06:49 UTC
[CentOS] Software RAID10 - which two disks can fail?
On Tuesday, April 08, 2014 03:47 AM, Rafa? 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