| Spelic | Absymal performance of O_DIRECT write on parity raid
Hi all linux raiders
on kernel 2.6.36.2, but probably others, performances of O_DIRECT are
absymal on parity raid, compared to nonparity raid
And this is NOT due to the RMW apparently! (see below)
With dd bs=1M to the bare MD device, a 6-disk raid5 1024k chunk, I
obtain 2.1MB/sec on raid5 while the same test onto a 4-disk raid10 goes
at 160MB/sec (80 times faster).
even with stripe_cache_size to the max.
Nondirect writes to the arrays are at about 250MB/sec for raid5, and
about ...
| Dec 30, 9:35 pm 2010 |
| Doug Dumitru | Re: Absymal performance of O_DIRECT write on parity raid
A couple of comments.
First, your test stripe size is very large. With 6 disks raid-5 and
1M chunks, you need 5MB of IO to fill a stripe. With direct IO, the
IO must complete and "sync" before dd continues. Thus each 1M write
will do reads from 4 drives and then 2 writes. I am not sure about
iostat not seeing this. I ran this here against 8 SSDs.
test file: 1G of random data copied from /dev/urandom into /dev/shm
(ssds can vary speed based on data content, hdds don't tend to act
this ...
| Dec 30, 10:36 pm 2010 |
| Mark Knecht |
| Dec 30, 5:14 pm 2010 |
| Mark Knecht | Why does md3 persist after deleting and recreating the p ...
Hi,
What am I forgetting to do? I had a RAID1 using sd{a,b,c}3. I
stopped md3, removed the md3 line in /etc/mdadm.conf, deleted the
partitions using fdisk, and then created 5 new partitions using
sd{a,b,c,d,e}3 to get ready to do a 5 disk RAID6. The new partitions
are the same size as the old ones and located at the same sector
addresses.
After rebooting, but before creating the new RAID6, I still see md3:
mark@c2stable ~ $ cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] ...
| Dec 30, 5:10 pm 2010 |
| Mathias Burén |
| Dec 30, 5:12 pm 2010 |
| Mathias Burén |
| Dec 30, 5:16 pm 2010 |
| Mark Knecht |
| Dec 30, 5:17 pm 2010 |
| Neil Brown | Re: Why does md3 persist after deleting and recreating t ...
That sentence doesn't make much sense to me, so I suspect some misunderstand
is going on. So to be explicit:
Use
mdadm --zero-superblock /dev/sdc3 /dev/sdb3 /dev/sda3
to remove from those devices any record that they are part of any md array.
Does that clarify thing sufficienty?
NeilBrown
--
| Dec 30, 6:07 pm 2010 |
| Mark Knecht |
| Dec 30, 6:33 pm 2010 |
| Jim Schatzman | Re: Why won't mdadm start several RAIDs that appear to b ...
After explicitly stopping the RAID (mdadm -S /dev/md5), and executing the mdadm -A --verbose command as suggested, more info is forthcoming. Mdadm appears to think that /dev/sdi5 and /dev/sdj5 are "busy". Since only /dev/sda5 and /dev/sdk5 can be added to the RAID, we are hosed.
I am puzzled as to why it thinks /dev/sdi5 and /dev/sdj5 are "busy". Fdisk reports normal partition data, dmesg and the system log report no problems, and I have no trouble copying data from /dev/sdi5 and /dev/sdj5 with dd. ...
| Dec 30, 8:38 pm 2010 |
| Jim Schatzman | Re: Why won't mdadm start several RAIDs that appear to b ...
All-
Using yum/rpm to remove dmraid from the system and rebooting fixed the problem.
Why is dmraid doing anything at all when my motherboard doesn't support FakeRAID? It seems that it is arbitrarily picking some set of drives to tie up, effectively disabling mdadm for some arrays. Nice.
Jim
--
| Dec 30, 8:51 pm 2010 |
| Neil Brown |
| Dec 30, 6:08 pm 2010 |
| Stan Hoeppner | Re: New raid level suggestion.
Sorry I was a bit prickly in my reply John. For some reason I became
defensive, and shouldn't have. Chalk it up to mood I guess.
It's entirely possible that I misunderstood Roger's requirements. I
believe he was talking about two different systems, one a transaction
type server in his first thread, the other just a web sever in this
thread. That's why I recommended the possibility of simple RAID 1 for
the web server.
It's difficult for me to imagine a web server scenario that would ...
| Dec 31, 3:23 am 2010 |
| Guy Watkins | RE: read errors corrected
} -----Original Message-----
} From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
} owner@vger.kernel.org] On Behalf Of James
} Sent: Thursday, December 30, 2010 8:48 PM
} To: Neil Brown
} Cc: linux-raid@vger.kernel.org
} Subject: Re: read errors corrected
}
} Neil,
}
} I'm runinng 2.6.35.
}
} Although an expensive route, the only thing I can think to do to
} determine 100% whether the issue is software or hardware (and, if
} hardware, whether SATA controller or the drives) is ...
| Dec 30, 6:56 pm 2010 |
| James | Re: read errors corrected
Neil,
I'm runinng 2.6.35.
Although an expensive route, the only thing I can think to do to
determine 100% whether the issue is software or hardware (and, if
hardware, whether SATA controller or the drives) is to swap the drives
out.
Ouch!
Any other ideas, however, would be appreciated before I drop a few
hundred bucks. :)
-james
--
| Dec 30, 6:48 pm 2010 |
| Neil Brown | Re: read errors corrected
Buy a PCIe SATA controller, plug it in and move some/all drives over to that?
Should be a lot less than $100. Make sure it is a different chipset to what
you have on your motherboard.
NeilBrown
--
| Dec 30, 7:08 pm 2010 |
