[mythtv-users] question about RAID
Johnathon Meichtry
johnathon-dev at meichtry.org
Mon Jan 9 20:55:24 UTC 2006
Steve,
My OS is Gentoo and the Logical Volume Manager I use is LVM2. To be honest
I don't know what the difference is between the mdadm tool and the various
tools which make up lvm2 it's just that I know how to use lvm2.
If you have two disks then I suppose you ought to use RAID1 and mirror them.
The down side is that you only get access to half the combined total disk
space. If you don't care about redundancy then you should use RAID0 as
RAID1 comes at a price (with software lvm) as everything needs to be done
twice (although I don't notice it on my server).
Johnathon
----- Original Message -----
From: "Steve Adeff" <adeffs at gmail.com>
To: <mythtv-users at mythtv.org>
Sent: Monday, January 09, 2006 8:16 PM
Subject: Re: [mythtv-users] question about RAID
On Monday 09 January 2006 14:32, Johnathon Meichtry wrote:
> ----- Original Message -----
> From: "Steve Adeff" <adeffs at gmail.com>
> To: <mythtv-users at mythtv.org>
> Sent: Monday, January 09, 2006 3:03 PM
> Subject: Re: [mythtv-users] question about RAID
>
> > On Sunday 08 January 2006 19:50, Gavin Haslett wrote:
> >> RAID 0 would be a straight stripe with no data protection. You were
> >> talking about three drives, so in order to use all three you'd be
> >> talking this or a RAID 5 in order to get some modicum of protection.
> >
> > I was under the impression RAID 0 was the fastest RAID, but has no data
> > protection? Is there no way to get RAID 0 to use more than one drive?
> > Like I
> > said, I'm not concerned with redundency on the RAID0 since I plan to
> > save
> > recordings I want to keep to a RAID5 array.
> >
> >> If you wanted to go RAID 1 or RAID 0+1 then you'd need an even number
> >> of
> >> drives, and total capacity would be half the actual aggregate capacity
> >> of all those drives.
> >>
> >> Note that in order to create your RAID you're going to have to re-
> >> partition your existing disk... so a backup and restore is inevitable.
> >
> > My plan was to use the two new drives to setup the RAID0, copy the files
> > over
> > from my current drive, then remount everything so that the RAID0 becomes
> > my
> > recording directory.
> >
> >> I know you said data protection is not an issue... but believe me when
> >> I
> >> tell you that it can become an issue rapidly. You can build a
> >> significant collection of recordings on any reasonable size media (I
> >> have mirrored 160Gb drives myself), and there's no recovery if you lose
> >> a single disk. It's not like you can cut the array down to half the
> >> array and still get half your data back... you'll lose it all if one of
> >> the drives in a RAID 0 fails. RAID 5 and RAID 1/0+1 would at least
> >> allow
> >> you protection.
> >
> > Which is why I plan on a RAID5 for my archives drive. I'm hoping HD-DVD
> > makes
> > a large presence upon its release and I can just buy the shows I keep in
> > HD-DVD and not need to archive them for a long time.
> >
> >> >From a sheer cost perspective I'd say RAID 5 is the way to go... but
> >>
> >> bear in mind that the processing overhead of RAID 5 plus the data load
> >> of reading and writing data and parity in a RAID 5 will make it slow,
> >> especially since you run significant risk of saturating the PCI bus
> >> with
> >> SATA.
> >>
> >> My dual 160's work great for me right now, and if I wanted to expand
> >> I'd
> >> just add another pair of drives and continue my RAID 0+1 I set up. I
> >> have thought about buying a third and going RAID 5 (would double my
> >> storage). Since I'm running ATA133 instead of SATA (drives were cheaper
> >> at the time) I am not really stressed about saturating the bus... but
> >> my
> >> poor old AMD 800 might not be happy with me ;)
> >
> > --
> > Steve
> >
> >
> Steve,
>
> All RAID0 does is join (or grow) partitions together. It is very useful
> if
> you have, for example, three 100GB disks about like them joined into a
> 300GB partition.
>
> What I have is follows on my Master Backend:
>
> Root Disk (/boot, /,Swap and /cache for ringbuffer ): Dual 160GB
> SATA disks mirrored (RAID1 using Logical Volume Manager). /cache has 92GB
> allocated for the ringbuffer.
> Media Disk Array (/mnt/store): Intel SATA 6 Port RAID PCI card
> with 4 x 500GB SATA disks in hardware RAID5 array mounted as one 1500GB
> partition. All rippped DVD's and TV are stored on this partition along
> with a whole bunch of non-Myth stuff such as personal files etc.
which is roughly what I would like to do (well, maybe not 500GB quite yet).
I'll have to see if I can get more than 2 disks for the RAID1 array, if not,
hopefully 2 will be fast enough for what I need.
I notice you are using LVM for your RAID1, why did you choose this over
mdadm?
> Since I have a mix of hardware and software RAID I must say that I don't
> notice a performance benefit between either i.e. they seem to perform
> about
> the same and are about as reliable as each other. The benefit to the
> hardware raid card is that it gives me 6SATA ports with no CPU performance
> hit and I keep two ports spare in case I need to grow/add disks or replace
> failures. The moral is to use whatever suits your situation, budget or
> available hardware - both work just as well as the other.
>
> If I can recommend anything to anyone about disks it is to go down the
> SATA
> route. They are hot swappable (i..e even if it doesn't say hot-sweappable
> on the packaging you can plug in a SATA disk while the server is on) and
> secondly get a PCI-Express SATA controller as normal PCI quickly becomes a
> bottleneck on media servers. I am yet to find a PCI-Express x16 SATA
> controller but once I do I will be buying it as it would be many times
> faster than PCI and finally allow the drives to work at speeds they were
> designed for. That's just my two cents worth for IDE vs. SCSI vs. PATA
> vs.
> SATA vs. Hardware RAID vs. Software RAID.
=) already going down this route, all my new drives are SATA. I'm also going
to wait for a PCI-Express x16 SATA controller before I bother buying one,
same reasons as you.
> One more thing ... never forget MTBF (mean time before failure) ... every
> drive has one, and is probably something like 100,000 hours on an old
> drive
> and the more you use the disk the closer you get to it ...my point is that
> systems like MythTV have the disks working a heck of a lot if not
> constantly therefore getting forever closer to your MTBF so use old disks
> with a touch of caution and be prepared to lose whatever is on it.
>
> Regards,
>
> Johnathon
--
Steve
_______________________________________________
mythtv-users mailing list
mythtv-users at mythtv.org
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
More information about the mythtv-users
mailing list