[GLLUG] Software RAID advice

John Winters john at sinodun.org.uk
Sat Jan 6 16:42:52 UTC 2018

On 06/01/18 15:02, Imran Chaudhry via GLLUG wrote:
> I'm setting up a new server which I'm going to be sysadmining on an
> ad-hoc basis.
> One requirement is RAID and looking into software RAID/mdadm leaves me
> a little confused. All the examples I looked at put the system
> directories (eg. / and /boot etc) on a non-RAID partition and the rest
> /var /home on RAID.
> I'm assuming I can use software RAID across entire devices right?
> I'm aiming for between 2Tb and 4Tb of space. What RAID level would you
> recommend for least noise/least amount of overall maintenance.

If that's all you need in the way of disk space, definitely go for RAID 
1.  You might also want to consider having a couple of SSDs (again RAID 
1) for your system, reserving your 2TB/4TB spinning rusts for your data.

Personally, I tend to create 2 partitions on my system disks (3 if 
you're using UEFI booting) - a small (256M) partition for /boot, and 
then the rest of the disk as one large partition.

Create 2 RAID1 devices.  The first joins your two (one on each disk) 
256M partitions and is used directly for /boot.

The second joins your two remaining large partitions and is used as a 
physical volume for LVM.

Then under LVM, create your root, var, tmp, home and swap partitions as 
logical volumes sitting on your RAID1 physical volume.  (Systemd gets 
upset and moans if you have separate root and usr partitions.)  Leave 
some space unused so you have room to adjust things later on if needs be.

If you're using SSD for the system disks, create a single large 
partition on each HDD, RAID1 them, and then put home there instead of on 
your SSD RAID.

You can install your boot loader on both system disks, each pointing to 
its own copy of the boot partition.  That way you can still boot your 
system even if one of your system disks goes west.

On the quietness front, there are four things which are going to 
generate noise:

Case fans
PSU fan
CPU fan
Hard disc drives

For a quiet box, I'd go to QuietPC and pick a good case with quiet fans.

Pick a good quality PSU with a large, slow, variable speed fan.

You can get a completely fanless motherboard like this one - 
http://www.mini-itx.com/store/~J3160-ITX - with which I've had good 
results.  Very low power consumption too (although it's currently 
showing a long lead time).

SSDs obviously are completely silent.  For your HDDs, try to get a case 
with decoupling mounts for the drives.  If you use them just for data 
then you can arrange for them to spin down when unused.

Interested in Martin's suggestion of using EC2.  Martin - can you give 
some indication of what it would cost to have 4TB of storage like this 
in the cloud?


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