Vidura Senadeera
2007-Aug-21 10:34 UTC
[asterisk-users] Saftware RAID1 or Hardware RAID1 with Asterisk (Vidura Senadeera)
> >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... > >-------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.digium.com/pipermail/asterisk-users/attachments/20070821/b482907e/attachment.htm
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