From: Luke Lonergan <llonergan@greenplum.com>
To: Dimitri <dimitrik.fr@gmail.com>
To: Craig James <craig_james@emolecules.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Autodetect of software RAID1+0 fails
Date: Fri, 01 Jun 2007 12:54:44 -0700
Message-ID: <C285C794.3219A%llonergan@greenplum.com> (raw)
In-Reply-To: <5482c80a0706011151y3851c68je5829a2291282b73@mail.gmail.com>
Dimitri,
LVM is great, one thing to watch out for: it is very slow compared to pure
md. That will only matter in practice if you want to exceed 1GB/s of
sequential I/O bandwidth.
- Luke
On 6/1/07 11:51 AM, "Dimitri" <dimitrik.fr@gmail.com> wrote:
> Craig,
>
> to make things working properly here you need to create a config file
> keeping both raid1 and raid0 information (/etc/mdadm/mdadm.conf).
> However if your root filesystem is corrupted, or you loose this file,
> or move disks somewhere else - you are back to the same initial issue
> :))
>
> So, the solution I've found 100% working in any case is: use mdadm to
> create raid1 devices (as you do already) and then use LVM to create
> raid0 volume on it - LVM writes its own labels on every MD devices and
> will find its volumes peaces automatically! Tested for crash several
> times and was surprised by its robustness :))
>
> Rgds,
> -Dimitri
>
> On 6/1/07, Craig James <craig_james@emolecules.com> wrote:
>> Apologies for a somewhat off-topic question, but...
>>
>> The Linux kernel doesn't properly detect my software RAID1+0 when I boot up.
>> It detects the two RAID1 arrays, the partitions of which are marked
>> properly. But it can't find the RAID0 on top of that, because there's no
>> corresponding device to auto-detect. The result is that it creates /dev/md0
>> and /dev/md1 and assembles the RAID1 devices on bootup, but /dev/md2 isn't
>> created, so the RAID0 can't be assembled at boot time.
>>
>> Here's what it looks like:
>>
>> $ cat /proc/mdstat
>> Personalities : [raid0] [raid1]
>> md2 : active raid0 md0[0] md1[1]
>> 234436224 blocks 64k chunks
>>
>> md1 : active raid1 sde1[1] sdc1[2]
>> 117218176 blocks [2/2] [UU]
>>
>> md0 : active raid1 sdd1[1] sdb1[0]
>> 117218176 blocks [2/2] [UU]
>>
>> $ uname -r
>> 2.6.12-1.1381_FC3
>>
>> After a reboot, I always have to do this:
>>
>> mknod /dev/md2 b 9 2
>> mdadm --assemble /dev/md2 /dev/md0 /dev/md1
>> mount /dev/md2
>>
>> What am I missing here?
>>
>> Thanks,
>> Craig
>>
>> ---------------------------(end of broadcast)---------------------------
>> TIP 1: if posting/reading through Usenet, please send an appropriate
>> subscribe-nomail command to majordomo@postgresql.org so that your
>> message can get through to the mailing list cleanly
>>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/docs/faq
>
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: llonergan@greenplum.com, dimitrik.fr@gmail.com, craig_james@emolecules.com
Subject: Re: Autodetect of software RAID1+0 fails
In-Reply-To: <C285C794.3219A%llonergan@greenplum.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox