XLV JBOD volume as a startup disk?

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pablodiablo
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XLV JBOD volume as a startup disk?

Unread postby pablodiablo » Mon Jul 16, 2007 1:10 pm

Is it possible to build a volume from several disks and make it a startup disk in irix to achieve better performance?
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SAQ
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Re: XLV JBOD volume as a startup disk?

Unread postby SAQ » Mon Jul 16, 2007 2:02 pm

pablodiablo wrote:Is it possible to build a volume from several disks and make it a startup disk in irix to achieve better performance?


Granted that I'm new to this, I've just used lvm managers to concatenate small disks into one bigger root filesystem, but where would the speed benefit come from? It's not like a RAID, where data is semi-evenly distributed.

Answering your question: I don't think it would work. AFAIK sash doesn't support logical volumes of any type other than plexes/mirrors.
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shel
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Re: XLV JBOD volume as a startup disk?

Unread postby shel » Mon Jul 16, 2007 2:30 pm

pablodiablo wrote:Is it possible to build a volume from several disks and make it a startup disk in irix to achieve better performance?

Probably not, since the combined volume doesn't exist before IRIX is loaded. I.e. before IRIX loads the XLV software, those individual disks are just individual disks.

This is a problem with any sort of software disk manipulation, whether it's XLV, some software RAID thing, whatever, under any OS. Until the OS loads, you don't have the software to do RAID, XLV, etc.

-Shel

anotheradamdickson
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Re: XLV JBOD volume as a startup disk?

Unread postby anotheradamdickson » Mon Jul 16, 2007 3:46 pm

shel wrote:
pablodiablo wrote:Is it possible to build a volume from several disks and make it a startup disk in irix to achieve better performance?

Probably not, since the combined volume doesn't exist before IRIX is loaded. I.e. before IRIX loads the XLV software, those individual disks are just individual disks.

This is a problem with any sort of software disk manipulation, whether it's XLV, some software RAID thing, whatever, under any OS. Until the OS loads, you don't have the software to do RAID, XLV, etc.

-Shel


As soon as the IRIX kernel is loaded with the support for the disks you'll have filesystem support so you can mount. It's a pain the ass and I don't know if it's 'supported' but you can use a normal disk (or one of the XLV disks as long as the ARC PROM on the SGI can boot from it) just to provide a disk label and device for the PROM to load the disk label/kernel.

Once the kernel is loaded you could mount the new volume as root. However it wouldn't be that hot an idea of your just catenating disks because there would be no increase in speed (well maybe if a file spans the disks there could be a small speedup) and it would only take one disk to failure to kill your machine. If your using strpped disks you'ld get a rather large speedup and again if you lost a disk you'ld lose your root file system. RAID5-style would get you some speedup normally but would slow down greatly if you lost a disk and the normally speedup wouldn't be that large anyway

What *exactly* are your planning and are you planning on doing it with controllers that are supported and can boot from the ARC PROM ???? (IE: do the disks show up in the PROM's hinv ???. Stuff like a XIO FC controller will show up - but their disks won't - it's only ID'ing the contoller not init'ing and using it for boot devices)

For the most part normally stripped/mirrored disks are just mounted onto a normal root volume. When reliability and speed becomes very important then often the root volume is on an external RAID box is used so to calculate RAID5/parity information and still provide a large speedup. These boxes often have redundant options for power supplies and controllers which is a further ensures no single point of failure

You can *easily* still create a new stripped volume copy the /usr tree over to it and then edit /etc/fstab to mount the new volume over /usr. The machine will have no problems booting and will stil get a fairly large speedup from much of the data on a different/stripped volume. This way you wouldn't have to get the NVRAM or play games with having a PROM bootable disk and disk label with kernel to boot from either. If the stripped volume fairs you'll get allot of errors and the programs you've installed on the new volume won't work - and your system will be messed up abit but you'll still have a GUI and be able to figure out what's going on in the event of a failure

It's good the keep in mind that stripes are much more prone to failure and unless you have hardware, extra disks and free CPU's to handle the overhead for an redundant filesystem adding a parity disk will kill most of the performance of stripped disks to begin with (unless - again if you have an external RAID box to do all the work for the host and just present the RAID as a normal disk to IRIX). Even RAID volumes on average will need more care & feeding in the long run then a single drive - and their be more disks failing. However as long as the disks are replaced the chance of losing everything is lower. If you don't have any hotspares and you don't have somebody to replace failed drives on average the RAID would be *AT LEAST* as likely to fail over many years then a single drive. However in the short term even - even if nobody is there to change failed disks RAID's will provide - RAID's will provide some protection against the flukely one time premature failures (because it's unlikey for all to fail prematurely - ah - unless their Maxtor 200Gig 10K IDE drives then their all likely to fail in an officaly unlikely 'premature' failure) . but overall in the end with a RAID there's more drives to fail and if the failed drives aren't replaced in a timely fashion your more likely to have a complete volume failure and lose everything- you just can't mess with the stats

IRIX 'load balances' the swap partition and files - so you don't need to have a stripped disk to get the memory swapping speedup of the added throughput. Just add the swap with the same preference and IRIX will use them in a parallel manner to increase the swap throughput. Swap partition have lower overhead and latency then using a file - so it's advisable never to use swap files if it can be at all helped - the overhead is quite noticeable on machines that are routinely swapping large amounts of RAM in and out

LoWeN
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Re: XLV JBOD volume as a startup disk?

Unread postby LoWeN » Tue Jul 17, 2007 12:48 am

Hello,

Sgi is only supporting mirroring for the root fs.
No stripping which sounds logical since the system would write the kernel with stripes and
would be unable to read it at boot time since the prom can't handle stripes.
That speed up a bit the system because you can read and write in parallel but this mainly to prevent downtime or loss of data.

@+

LoWeN
UX powered

pablodiablo
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Re: XLV JBOD volume as a startup disk?

Unread postby pablodiablo » Tue Jul 17, 2007 3:26 am

Well, I was just thinking of making some speed improovment using additional space for drives in my Onyx2. I'm using also PowerMac G5 and in this machine I have startup disk that is made of two physical drives, and system runs much smoother and faster. It was quite easy to build this volume and OSX was installed like on normal drive, so I hoped it would be also possible in other unix :)
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anotheradamdickson
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Re: XLV JBOD volume as a startup disk?

Unread postby anotheradamdickson » Tue Jul 17, 2007 8:49 am

pablodiablo wrote:Well, I was just thinking of making some speed improovment using additional space for drives in my Onyx2. I'm using also PowerMac G5 and in this machine I have startup disk that is made of two physical drives, and system runs much smoother and faster. It was quite easy to build this volume and OSX was installed like on normal drive, so I hoped it would be also possible in other unix :)


It may be safer/easier just to mount /usr on a stripped volume. The IRIX machine is the best OS (performance wise) I've used for software stripped/mirroring performance. It will give it a faster speed then the MAC.

Mirring is nice because you get double the read speed because you can be seeking different sectors from each drive. However there's a bit of a slowdown on writes because you now must make Nx amount of copies to each mirror each time you write/change data on the filesystem. This is being done with SCSI controllers though - so it's not a huge load on the machine. But it can be a bottleneck on the SCSI controller. There's no copying involved on the host - it just puts the data in a buffer and then writes the same buffer to each disk

If you can deal with the space waste and read performance is more important then write performance then mirror'ing may be the way to go for you

MIrror/stripped over large numbers of disk on IRIX (and Linux) can often make rather large/insane speedup that are almost the max of each hard disk added together. Unlike windows where there's less then %99 percent speed increase for the first striped and diminishing returns after that.

SAQ
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Re: XLV JBOD volume as a startup disk?

Unread postby SAQ » Tue Jul 17, 2007 9:13 am

Never tried it, but one possibility may be to use a setup similar to HP-UX: make a small /boot partition, format it XFS and stash the kernel in it. Then with the second partition on the main drive and a second drive you can stripe the root filesystem. Mirroring is great, but remember that on IRIX it's an extra-cost option, and knowing SGI that extra cost is going to be substantial.
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anotheradamdickson
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Re: XLV JBOD volume as a startup disk?

Unread postby anotheradamdickson » Tue Jul 17, 2007 12:58 pm

SAQ wrote:Never tried it, but one possibility may be to use a setup similar to HP-UX: make a small /boot partition, format it XFS and stash the kernel in it. Then with the second partition on the main drive and a second drive you can stripe the root filesystem. Mirroring is great, but remember that on IRIX it's an extra-cost option, and knowing SGI that extra cost is going to be substantial.


Well many of us may already be licensed for PLEXING. Espc big machines - if you goto the key-o-matic you can see if your machine serial has ever been issued with licenses and then get it reissued. Plus ... uh ..... geee ... ummm ....

Sometimes when buying machines on Ebay I've check just to see what licenses they have before taking the plunge - that was awhile back now though and SGI may of stopped the key-o-matic vampirism. But that was when I was new to SGI's too

The only machine that really surprised me was an O2 in stunning condition (but with bad MB, power supply I believe)

When I just started using the case/bp because it looked good and when I checked the number it had a fair amount of goodies already licensed. *Plexing* all of WorkShop and MipsPro kind of an odd combo. Never really figured that one out - compiling aways would seem to be I/O bound. Humpf - who knows I guess they used it for more then one thing


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