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Re: [PLUG] help me design my server
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Do you then run a risk of losing those tables if you lose power? I assume you've got batteries (or maybe you have a generator) - but wouldn't it take a LONG time to sync the disks on shutdown?
What numbers should I look for with iostat?
----- Original Message -----
From: John Von Essen <john@essenz.com>
To: Philadelphia Linux User's Group Discussion List <plug@lists.phillylinux.org>
Sent: Friday, September 14, 2007 1:20:29 PM GMT-0500
Subject: Re: [PLUG] help me design my server
Ok, so in that case the extra RAM on the host will help with disk IO and will cache data coming back from the controller - so less IO requests will be issued to the disk, the VM Ram doesn't need to be touched.
When I did this on a large postgres environment, it made a big difference. Prior, the machine had 8Gb, 6.5Gb of which was dedicated to postgres. iostats were awful. When upgrade to 16Gb Ram, postgres still only used 6.5Gb, but almost 10Gb of ram was available for the kernel to cache IO requests.
It helped so much that stress testing disk performance was difficult, after 20 seconds of running almost nothing was being issued to the controller, everything was coming out of ram. We had to re-write the benchmark apps so that every request was more unique and data set was larger then ram.
-John
On Sep 14, 2007, at 12:43 PM, W. Chris Shank wrote: The VMs use disk files on the host filesystem. So the host talks to the SATA controller directly.
----- Original Message -----
From: John Von Essen <john@essenz.com>
To: Philadelphia Linux User's Group Discussion List <plug@lists.phillylinux.org>
Sent: Friday, September 14, 2007 12:17:10 PM GMT-0500
Subject: Re: [PLUG] help me design my server
How does the VM access the storage?
Not sure which kernel context talks to the SATA controller. But whichever kernel does that, thats the one that needs more ram so it can do caching on the IO requests being sent to the controller.
-John On Sep 14, 2007, at 11:41 AM, W. Chris Shank wrote: I'm going to do that - but there isn't really any swapping on the host OS. Or are you saying more virtual RAM on the VM?
----- Original Message -----
From: John Von Essen <john@essenz.com>
To: Philadelphia Linux User's Group Discussion List <plug@lists.phillylinux.org>
Sent: Friday, September 14, 2007 11:32:13 AM GMT-0500
Subject: Re: [PLUG] help me design my server
Forget to mention, increasing RAM will make a significant difference. The kernel caching will alleviate alot of disk IO since those requests will be processed right from cache. Performance of increased memory is somewhat dependent on how you use your disk, i.e. heavy reads of common data vs random data.
-John
On Sep 14, 2007, at 11:28 AM, John Von Essen wrote: Chris,
The SATA arrays will always poor IO performance in environments like yours. I have some experience from going through issues with an 8-core Postgres server with heavy disk IO problems.
SCSI Raid will be better, especially if you have alot of spindles. Raid 10 instead of Raid 5 etc.,. And if you split it up across both channels of a dual channel card or spit it across multiple cards, that will help too. Problem is size limitations of SCSI raid 10 due to the numbers of drive slots in most external enclusores. 14-bay enclosure with Raid 10 and 146Gb drives will give about 1Tb. I wouldn't recommend using the 300Gb scsi drives. Smaller the drive, the better.
Eventually, SCSI will also break down. When that happens, you'll start to need a Fibre-Channel attached SAN, one specifically designed for high IO environments. The EMC Clarrions are getting a little better in price, but still pricy when compared to SATA arrays.
You may never need the EMC-level performance, so SCSI Raid with alot of spindles and good HBA controller management might do the trick for awhile.
-John On Sep 14, 2007, at 10:50 AM, W. Chris Shank wrote: I need to spec-out and architect another VMWare and/or Xen VM host server. Currently I have one with 8 cores, 4GB ram, and 1.5TB HDD as 4 500GB SATA with hardware raid5. We are starting to hit the wall with this setup running 5 VMs on it. Particularly, it seems the HDD I/O is the bottleneck. If one VM hits the disks hard it makes the others pretty much useless.
So I have a budget to get another honking server. I'm confident the quad-core Xeons with the vm extensions are sufficient. I'll go ahead and bump the RAM to 16G too. The area I'm most concerned with is the disk I/O. I'm thinking that instead of one big RAID5, I'll pair smaller drives - so i'll have 4 sets of 2 250G SATA mirrors. Then direct it so that 2-3 VMs are on each raid. Or should I go SCSI and keep one large RAID5?
So if you had the $$, what would you get and how would you configure it.
Thanks
--
W. Chris Shank
ACE Technology Group, LLC
www.myremoteITdept.com
(610) 640-4223
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___________________________________________________________________________ ___________________________________________________________________________
--
W. Chris Shank
ACE Technology Group, LLC
www.myremoteITdept.com
(610) 640-4223
--------------------------------
Security Note: To protect against computer viruses,
e-mail programs may prevent sending or receiving
certain types of file attachments. Check your e-mail
security settings to determine how attachments are
handled.
___________________________________________________________________________
--
W. Chris Shank
ACE Technology Group, LLC
www.myremoteITdept.com
(610) 640-4223
--------------------------------
Security Note: To protect against computer viruses,
e-mail programs may prevent sending or receiving
certain types of file attachments. Check your e-mail
security settings to determine how attachments are
handled.
___________________________________________________________________________
--
W. Chris Shank
ACE Technology Group, LLC
www.myremoteITdept.com
(610) 640-4223
--------------------------------
Security Note: To protect against computer viruses,
e-mail programs may prevent sending or receiving
certain types of file attachments. Check your e-mail
security settings to determine how attachments are
handled.
___________________________________________________________________________
Philadelphia Linux Users Group -- http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
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