[opensuse] Curious about different software raid signatures in top (md & dm raid)
Listmates, I am curious. I have several boxes that have regular software raid (mdraid) and several boxes that make use of bios raid (dmraid). Looking at top on the boxes with mdraid I notice that once every second or so the disks in the array are 'talking?' to each other which produces and nice rhythmic signature in top like: 1931 root 10 -5 0 0 0 S 0.7 0.0 4:59.63 md2_raid1 1090 root 10 -5 0 0 0 S 0.3 0.0 2:44.20 md1_raid1 Noticing this I checked the bios raid boxes to see if they had a similar indication in top. They don't. I know both md and dm raid are different software raid implementations for all practical purposes, but I was curious why md raid would show up in tom and dmraid doesn't. Does anybody have a one or two line synopsis they could share? Next, when I see the mdraid make its fleeting appearance in top, what is actually going on with the array? Guessing, it would appear that as part of the normal operation, the disks in the array (md1_raid1 & md2_raid1, here) are checking sync status and seeing if anything new has appeared that needs to be duplicated from one disk to the other. Is that all that is going on or its it something else? It's a good thing I'm not a cat, it would have killed me a long time ago;-) -- David C. Rankin, J.D.,P.E. Rankin Law Firm, PLLC 510 Ochiltree Street Nacogdoches, Texas 75961 Telephone: (936) 715-9333 Facsimile: (936) 715-9339 www.rankinlawfirm.com -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
Hi there, On Fri, 13 Feb 2009, 04:51:49 +0100, David C. Rankin wrote:
Listmates,
I am curious. I have several boxes that have regular software raid (mdraid) and several boxes that make use of bios raid (dmraid). Looking at top on the boxes with mdraid I notice that once every second or so the disks in the array are 'talking?' to each other which produces and nice rhythmic signature in top like:
1931 root 10 -5 0 0 0 S 0.7 0.0 4:59.63 md2_raid1 1090 root 10 -5 0 0 0 S 0.3 0.0 2:44.20 md1_raid1
Noticing this I checked the bios raid boxes to see if they had a similar indication in top. They don't. I know both md and dm raid are different software raid implementations for all practical purposes, but I was curious why md raid would show up in tom and dmraid doesn't. Does anybody have a one or two line synopsis they could share?
Next, when I see the mdraid make its fleeting appearance in top, what is actually going on with the array? Guessing, it would appear that as part of the normal operation, the disks in the array (md1_raid1 & md2_raid1, here) are checking sync status and seeing if anything new has appeared that needs to be duplicated from one disk to the other. Is that all that is going on or its it something else?
It's a good thing I'm not a cat, it would have killed me a long time ago;-)
Looks like you're using a write-intent bitmap for your md-raid1's, which is used to limit the amount of data to be re-synchronized in the case something went wrong with one of the raid1 devices. I'd suggest looking at the details of your md-raid1: mdadm -Q -D /dev/md1 If it contains an indication about the use of an "Intent Bitmap", then you know what's causing the traffic. If you don't want it to happen, you can turn it off again with mdadm --grow /dev/md1 --bitmap=none which will cause a full resync in case a device of that md-raid1 device is happening to fail. Full details in the mdadm manual page. HTH, cheers. l8er manfred -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
Manfred Hollstein wrote:
Hi there,
On Fri, 13 Feb 2009, 04:51:49 +0100, David C. Rankin wrote:
Listmates,
I am curious. I have several boxes that have regular software raid (mdraid) and several boxes that make use of bios raid (dmraid). Looking at top on the boxes with mdraid I notice that once every second or so the disks in the array are 'talking?' to each other which produces and nice rhythmic signature in top like:
1931 root 10 -5 0 0 0 S 0.7 0.0 4:59.63 md2_raid1 1090 root 10 -5 0 0 0 S 0.3 0.0 2:44.20 md1_raid1
Noticing this I checked the bios raid boxes to see if they had a similar indication in top. They don't. I know both md and dm raid are different software raid implementations for all practical purposes, but I was curious why md raid would show up in tom and dmraid doesn't. Does anybody have a one or two line synopsis they could share?
Next, when I see the mdraid make its fleeting appearance in top, what is actually going on with the array? Guessing, it would appear that as part of the normal operation, the disks in the array (md1_raid1 & md2_raid1, here) are checking sync status and seeing if anything new has appeared that needs to be duplicated from one disk to the other. Is that all that is going on or its it something else?
It's a good thing I'm not a cat, it would have killed me a long time ago;-)
Looks like you're using a write-intent bitmap for your md-raid1's, which is used to limit the amount of data to be re-synchronized in the case something went wrong with one of the raid1 devices.
I'd suggest looking at the details of your md-raid1:
mdadm -Q -D /dev/md1
If it contains an indication about the use of an "Intent Bitmap", then you know what's causing the traffic. If you don't want it to happen, you can turn it off again with
mdadm --grow /dev/md1 --bitmap=none
which will cause a full resync in case a device of that md-raid1 device is happening to fail. Full details in the mdadm manual page.
HTH, cheers.
l8er manfred
Manfred, Good to be with you. You nailed it! root@zion:/home/david # mdadm -Q -D /dev/md1 /dev/md1: Version : 01.00.03 Creation Time : Sun Jun 22 01:40:26 2008 Raid Level : raid1 Array Size : 467411004 (445.76 GiB 478.63 GB) Used Dev Size : 934822008 (891.52 GiB 957.26 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 1 Persistence : Superblock is persistent Intent Bitmap : Internal ^^^^^^^^^^^^^^^^^^^^^^^^ Update Time : Sun Feb 15 23:27:24 2009 State : active Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Name : 1 UUID : b119e184:e3bd8652:792c1ed2:3107e924 Events : 12 Number Major Minor RaidDevice State 0 8 54 0 active sync /dev/sdd6 1 8 38 1 active sync /dev/sdc6 I'll go digest man mdadm a bit more. In the mean time, I there any benefit to keeping it or removing it? I figure it is there for a reason, but what to you see in the real world. -- David C. Rankin, J.D.,P.E. Rankin Law Firm, PLLC 510 Ochiltree Street Nacogdoches, Texas 75961 Telephone: (936) 715-9333 Facsimile: (936) 715-9339 www.rankinlawfirm.com -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
Hi David, On Mon, 16 Feb 2009, 06:29:55 +0100, David C. Rankin wrote:
[...] root@zion:/home/david # mdadm -Q -D /dev/md1 /dev/md1: Version : 01.00.03 Creation Time : Sun Jun 22 01:40:26 2008 Raid Level : raid1 Array Size : 467411004 (445.76 GiB 478.63 GB) Used Dev Size : 934822008 (891.52 GiB 957.26 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 1 Persistence : Superblock is persistent
Intent Bitmap : Internal ^^^^^^^^^^^^^^^^^^^^^^^^ Update Time : Sun Feb 15 23:27:24 2009 State : active Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0
Name : 1 UUID : b119e184:e3bd8652:792c1ed2:3107e924 Events : 12
Number Major Minor RaidDevice State 0 8 54 0 active sync /dev/sdd6 1 8 38 1 active sync /dev/sdc6
I'll go digest man mdadm a bit more. In the mean time, I there any benefit to keeping it or removing it? I figure it is there for a reason, but what to you see in the real world.
It depends... I once had trouble because one disk repeatedly failed and got kicked from the mirror; when I checked the disk it appeared OK, so I re-added it to the mirror which resulted again in a full resync. I eventually found out that it wasn't the disk, but the cables which caused connectivity to be flaky. Bitmaps definitely help in keeping synchronization times to a minimum. In my experience you don't need it very often in your home environment - assuming you're using high quality cables ;-) - while it's an absolute must-have e.g. in a cluster environment where you must fail-over the mirror from time to time and have to live with asynchronous drops between the storage elements. FWIW, I have bitmaps enabled on all my systems. HTH, cheers. l8er manfred -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
participants (2)
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David C. Rankin -
Manfred Hollstein