[asterisk-users] Saftware RAID1 or Hardware RAID1 with Asterisk (Vidura Senadeera)

Tue Aug 21 05:34:06 CDT 2007

>
>

Dear all,

Thanks for the greate explanation regaing Software/H/W Raid. This details
better but on voip-info.org/wiki pages.

Thanks lot agian.
Regs,
Vidura Senadeera.

======================================

Dear All,
> >
> > I would like to get community's feedback with regard to RAID1 ( Software
> or
> > Hardware) implementations with asterisk.
> >
> > This is my setup
> >
> > Motherboard with SATA RAID1 support
> > CENT OS 4.4
> > Asterisk 1.2.19
> > Libpri/zaptel latest release
> > 2.8 Ghz Intel processor
> > 2 80 GB SATA Hard disks
> > 256 MB RAM
> > digium PRI/E1 card
> >
> > Following are the concerns I am having
> >
> > I'm planing to put this asterisk server in production enviorment which
> is
> > having E1 connection to the asterisk server, approximately
> > 20 con-current calls, Music on hold, voice mail boxes.
> >
> > 1. If I use Software RAID, what would be the impact to my deployment?
> > ( problems that I have to face with regard to the call flow )
> > 2. If I use Hardware based RAID 1, what would be the impact to the
> system?
> > 3. According to your practical experiance what is the ideal solution
> among
> > both options?
>
> With my other hat on I build and maintain many servers with disk
> capacities ranging from 80GB to over 6TB... All using Linux software RAID.
> I've been using Linux s/w RAID for over 8 years now.
>
> So with RAID-1 done in hardware, the impact to the system, CPU, etc.
> should be no more (or less) than running a single SCSI or SATA drive. You
> write the data over the (PCI) bus once and the hardware takes care of
> writing it to both drives behind your back. Similarly for reading (where
> it might only read from one drive or from alternative drives) you only see
> one transaction over the PCI bus.
>
> You do (sometimes) need the hardware RAID controller to be supported by
> Linux and this is a weak area. Some controllers just look like a standard
> drive, so they are transparent to the system, but then you need to use
> either the BIOS utilities to set it up in the first place, or (typically)
> a Windows utility, although some controllers are now being supported by
> Linux with user-land tools to manage and check the arrays.
>
> Doing it in software requires double the PCI bandwidth for writes, but the
> same as a single drive or hardware controller for reads. AIUI, the current
> software RAID-1 reads alternatively from the disks. So on writes. The
> overhead in terms of CPU power is minimal - write the same block twice,
> and if the hardware is good, then both writes can be transfered over the
> PCI bus rapidly, into the cache on the drives and the writes then take
> place in parallel, so performance wise, it's really no worse than single
> drive (and it's important to note than it's no better than a single drive
> on reads too, despite many threads on the linux-raid list suggesting
> otherwise!)
>
> RAID-1 doesn't require parity calculations, so the software overhead
> really is quite small (especially when you compare it to the relatively
> huge times it takes to actually get the data to/from the disks)
>
> So things that are important: Make sure the hardware to each drive is as
> independent as possible. Hard to do these days as there is probably only
> one SATA controller chip on the motherboard. You also need to see what
> happens when a drive dies - is it going to crowbar the entire SATA chip
> and block the other drive? Is the driver going to recognise it quickly
> enough and so on. (Some early SATA drives weren't good at this)
>
> And the "usual" - make sure all the hardware has it's own interrupts.
>
> For the absolute maximun performance, (and minimum overheard) then you
> need a motherboard with multiple PCI buses - put the disks on one bus, the
> PRI card on another.
>
> If terms of disk b/w needed - if we're using g711, then it's 64KB/sec, and
> 20 calls streaming to voicemail is 1.3MB/sec. A single modern drive ought
> to be able to sustain 60MB/sec read or writes, so there is plenty of
> overhead, as long as asterisk is relatively sensible about buffering disk
> write/reads (which I think it is)
>
> So I'd say "go for it", but do take the time, if possible to build a
> custom kernel for your hardware, and at the BIOS level, turn off all
> drivers that you won't be using - eg. on-board sound, then 2nd network
> port, USB (if you're not using it, don't enable it!) and so on, and make
> sure you have a custom compiled kernel for your exact hardware
> requirements with no modules loaded other than the Zap/TDM, etc., ones.
>
> And I'd also say "go for it" because I have similarly specd. servers doing
> similar tasks also running asterisk. I won't put a server in a remote data
> centre these days without it either booting off flash, or using at least
> RAID-1.
>
> Remember to put your swap on RAID-1 too.
>
> Here is one of my servers in a similar setup to yours:
>
> $ cat /proc/mdstat
> Personalities : [raid0] [raid1]
> md1 : active raid1 hdc1[1] hda1[0]
>       248896 blocks [2/2] [UU]
>
> md2 : active raid1 hdc2[1] hda2[0]
>       995904 blocks [2/2] [UU]
>
> md3 : active raid1 hdc3[1] hda3[0]
>       2000000 blocks [2/2] [UU]
>
> md5 : active raid1 hdc5[1] hda5[0]
>       38081984 blocks [2/2] [UU]
>
> md6 : active raid1 hdc6[1] hda6[0]
>       38708480 blocks [2/2] [UU]
>
> unused devices: <none>
>
> $ df -h
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/md1              236M   38M  186M  17% /
> tmpfs                 249M     0  249M   0% /dev/shm
> /dev/md3              1.9G  1.2G  643M  65% /usr
> /dev/md5               36G   29G  5.3G  85% /var
> /dev/md6               37G   30G  4.7G  87% /archive
>
> $ cat /proc/swaps
> Filename                                Type            Size    Used
> Priority
> /dev/md2                                partition       995896  326712  -1
>
> It has 2 x 80GB IDE drives and I've partitioned them (because that's my
> preference), but one thing I do, is name the md (RAID) partitons after the
> partition names, so md1 is /dev/hda1 and /dev/hdb1 and so on. Makes life
> easy if changing a drive.
>
>
> Gordon
> Ps. There appears to be asterisk version 1.2.24 now, although I must have
> missed the announcements from Digium about it...
>
> Pps. Stick another 256MB of RAM in it if possible. It'll only cost pennies
> and might help with buffering stuff like MoH - or even copy MoH, prompts,
> etc. into a RAM disk at boot time...
>
>
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