Thanks Alex. I think I've decided to go RAID 1+0 rather than RAID 5 as
I'm worried about the write speed.
I often record 3 or 4 channels at once and do see some "slow down" on OSD
responsiveness during this.
What's your experience with RAID5?
----- Original Message -----
From: Alex Betis
To: VDR Mailing List
Sent: Friday, November 13, 2009 1:03 AM
Subject: Re: mdadm software raid5 arrays?
Simon,
Pay attention that /boot can be installed only on a single disk or RAID-1
where every disk can actually work as a stand alone disk.
I personally decided to use RAID-5 on 3 disks with RAID-1 on 3xsmall
partitions for /boot and RAID-5 on the rest.
RAID-5 also allows easier expansion in the future.
On Tue, Nov 10, 2009 at 8:48 PM, Simon Baxter <linuxtv@xxxxxxxxxxxxx> wrote:
Thanks - very useful!
So what I'll probably do is as follows...
* My system has 4x SATA ports on the motherboard, to which I'll connect my
4x 1.5TB drives.
* Currently 1 drive is in use with ~30G for / /boot and swap and ~1.4TB
for /media
* I'll create /dev/md2, using mdadm, in RAID1 across 2 ~1.4TB partitions
on 2 drives
* move all active recordings (~400G) to /dev/md2
* split /dev/md2 and create a raid 1+0 (/dev/md1) using 4x partitions of
~1.4TB across 4 drives
At this point I have preserved all my data, and created a raid1+0 for
recordings and media.
I should now use the remaining ~100G on each drive for raid protection for
(root) / and /boot. I've read lots on the web on this, but what's your
recommendation? RAID1 mirror across 2 of the disks for / (/dev/md0) and
install grub (/boot) on both so either will boot?
On Tue, Nov 10, 2009 at 09:46:52PM +1300, Simon Baxter wrote:
What about a simple raid 1 mirror set?
Ok.. short comparison, using a single disk as baseline.
using 2 disks
raid0: (striping)
++ double read throughput,
++ double write throughput,
-- half the reliability (read: only use with good backup!)
raid1: (mirroring)
++ double read throughput.
o same write throughput
++ double the reliability
using 3 disks:
raid0: striping
+++ tripple read performance
+++ tripple write performance
--- third of reliability
raid1: mirroring
+++ tripple read performance
o same write throughput
+++ tripple reliability
raid5: (distributed parity)
+++ tripple read performance
- lower write performance (not due to the second write but due
to the necessary reads)
+ sustains failure of any one drive in the set
using 4 disks:
raid1+0:
++++ four times the read performance
++ double write performance
++ double reliability
please note: these are approximations and depending on your hardware
they may be off by quite a bit.
cheers
-henrik
_______________________________________________
vdr mailing list
vdr@xxxxxxxxxxx
http://www.linuxtv.org/cgi-bin/mailman/listinfo/vdr
