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pthyseba
27-Mar-2012, 14:27
Hello,


I'm trying to figure out the correct settings for a 7+1 (1TB SATA) RAID5 mdadm software RAID5 setup on SLES 11 SP1.

I'm having a few questions:

1) I notice that "pvcreate" does not support the "--dataalignment" option, which is referenced in several Linux software RAID howto's and wikis ??

2) What would be the best way to setup a ext3 filesystem, without LVM (see 1 - and I can live with it being a single big filesystem).

Currently, what I think about doing is:
a) On each of the 8 disks, create a single primary partition starting at sector 2048 (should solve 512/4096 byte sector stuff)

b) create a RAID5 array (without spare disk) using
mdadm -C /dev/md/mdraid5 --chunk 128 --level 5 -n 8 --force /dev/sda1 .... /dev/sdh1

c) create an ext3 filesystem on the RAID5 device as follows:
mkfs.ext3 /dev/md/mdraid5 -b 4096 -E stride=32,stripe-width=224

(according to 'man mkfs.ext3', stride is the number of filesystem blocks in a RAID chunk, which is 128k/4k = 32. stripe-width is the numer of filesystem blocks in one RAID data stripe, which is (8-1)*128k/4k = 224) about 12

Does anyone have a well-informed opinion about
i) the raid5 chunk size to use (I thought about 128k, this filesystem will mostly host large files, order of GB size)
ii) whether my ext3 parameter derivations make sense
iii) how you would do it (ie setup RAID5 software raid, highest performance possible for a large-file filesystem, on SLES 11 SP1 with 8 1TB SATA disks)
iv) why pvcreate in SLES 11 SP1 is missing the "--dataalignment" option, whether it would still be needed (or the equivalent of it in SLES 11 SP1, what is it?) when using LVM on the RAID5 device
v) is ext3 a good enough filesystem for what I want to do (or is ext3 + software raid5 in this setup bound to be sluggish)? Should I look into ext4/xfs for software raid5 on SLES 11 SP1?



Thanks in advance for your responses!
Pieter

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05-Apr-2012, 13:30
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KBOYLE
05-Apr-2012, 16:16
pthyseba wrote:

> iv) why pvcreate in SLES 11 SP1 is missing the "--dataalignment"
> option, whether it would still be needed (or the equivalent of it in
> SLES 11 SP1, what is it?) when using LVM on the RAID5 device
> v) is ext3 a good enough filesystem for what I want to do (or is ext3
> + software raid5 in this setup bound to be sluggish)? Should I look
> into ext4/xfs for software raid5 on SLES 11 SP1?

Hi Pieter,

You have asked a lot of questions. Perhaps no one feels qualified to
supply all the answers. I will comment on iv).

SLES11-SP2 is now available. I would consider installing the current
release. See the release notes:
http://www.novell.com/linux/releasenotes/x86_64/SUSE-SLES/11-SP2/#fate-306585-1

In SLES11-SP2, the pvcreate man pages shows that "--dataalignment" is a
valid option and, personally, I like LVM.

SLES11-SP2 now supports btrfs which may be more suitable to your needs.
You will have to decide.

The SLES11-SP2 release notes has this to say about ext4. I would not
consider using ext4 on a SLES11-SP1 system.



10.9. Read-only Support for the ext4 File System for Migration Purposes

To facilitate the migration of an ext4 file system to another,
supported file system, the SLE 11 SP2 kernel now contains a fully
supported ext4 file system module, which provides solely read-only
access to the file system.

If read-write access to an ext4 file system is still required, you may
install the ext4-writeable KMP (kernel module package). This package is
available in the online repository "SLES11-Extras" and contains a
kernel module that provides read-write access to an ext4 file system.
Be aware, that this kernel module is unsupported.

ext4 is not supported for the installation of the SUSE Linux Enterprise
operating system files

With SUSE Linux Enterprise 11 SP2 we support offline migration from
ext4 to the supported btrfs filesystem.



Regarding software RAID5 with SATA drives:

The main reason to consider this configuration is to avoid the cost of
a hardware RAID adapter. This configuration provides the lowest
performance of the various options open to you but it may be adequate
if you are more concerned about storage capacity and cost. Performance
will depend upon the characteristics of your server, the hard drives,
and how you access your data.

If you use SATA drives, they are not all created equal. Assuming you
don't already have your hard drives, I would recommend only using
"enterprise class" drives that are rated for 7x24 service. Since you
are concerned about performance, I would consider stepping up to 7200
rpm SAS drives, especially if you already have a SAS controller. The
cost is only slightly more than enterprise SATA drives.


--
Kevin Boyle - Knowledge Partner
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