Best Practice KVM LVM SSD SAS SATA Config

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Idiot_Savant
Posts: 4
Joined: 2014/12/26 19:25:06

Best Practice KVM LVM SSD SAS SATA Config

Post by Idiot_Savant » 2014/12/27 19:57:50

Hi~!

I have a production mail server running CentOS 6.4 and iRedMail (can't upgrade right now, iRedmail version for CentOS 7 not ready yet). The box has 32GB SATADOM and 1TB LSI SAS RAID1. Grub and /boot are on the SATADOM in a primary partition, / and swap is in 2 LVM groups (lv_root and lv_swap). I PV'd the unused partition space on the 32GB SATADOM with the RAID1 Array - oops :roll: . Now, I have upgraded this server hardware with RAM/CPU and added 512GB (4x256) Samsung 850 Pro SSD RAID 10 array. I also have 2 unused 1TB drives available identical to existing RAID1. I also made my root LV using all the available disk space (I know ok? :roll: ). I never expected this box to do anymore than it is. Lastly, I have partition alignment 'problems' when using fdisk -l but that can be another thread. Just a detail.

The plan is to Install Centos 7 minimal and run KVM then migrate the existing server into a virtual machine and migrate a couple other small boxes onto it (one is MS 2012 server and some of it needs SSD speed). Here is my quandary: I am unsure of the best way to implement these disks/arrays for hosting the virtualization files. I could make the two available 1TB disks into a RAID1 array, but I was hoping to empty the existing RAID1, delete the array and create a RAID 10 array out of them. Sorry for the question: What is best practice for mixing these arrays? I want to be able to use the SSD's for what it is best at and the rest I want to put on the SAS Disks. Right now, this what I am contemplating: Setup CentOS 7 on SSD array w/PV on remaining space but make smaller VG for / etc. Then I am going to set my image directory to? Also I want to end up w/swap on the SATADOM. OR I could migrate the existing install to the SSD array (dd the SATADOM to the SSDs, create new PV, shrink existing root VG and move it over etc.) lots of options, right? :) I am thinking its best to place my image directory on the SAS disks and then make SSD storage available to the guests. What do you think?

New to KVM I have done a lot of searching and RTFM, but there doesn't seem to be a "best practice" for allocating various storage types to KVM files and Guests. I am hoping this thread can become helpful to others using KVM and how to allocate storage to guests efficiently while at the same time providing me some insight into my own unique circumstance. TIA :D

aks
Posts: 3008
Joined: 2014/09/20 11:22:14

Re: Best Practice KVM LVM SSD SAS SATA Config

Post by aks » 2014/12/27 21:02:51

Is this what you're looking for (http://www-01.ibm.com/support/knowledge ... es_pdf.pdf)?

First hit on a google search for KVM best practices

Idiot_Savant
Posts: 4
Joined: 2014/12/26 19:25:06

Re: Best Practice KVM LVM SSD SAS SATA Config

Post by Idiot_Savant » 2014/12/27 21:39:42

Hey aks -TY~!

Actually I read that and its great information. Actually jump started my switch from Xen to KVM. Honestly, I am actually asking two questions: 1.) What would you do if you were me? and 2.) What are other admins doing as far as image files vs block devices in real world applications and how that relates to SSD and SAS/SATA media. Fortunately my client can survive some downtime on weekends for that email server. One area I did not mention is backup. While block I/O has better performance it doesn't have the advantages of file based VMs and some of these VMs will be on ext4 which can deal with sparse files and conserve space and certainly makes backups easier. From everything I have read there are many ways to implement and I have always taken the hybrid approach (but definitely a KISS and DEFAULTS FAN :) . Looking for some examples and logic as I have neither.

It seems that my partition error problem happens A LOT, hence the document's references to it. FWIW I am about to down the box and start by moving my current installation to the SSDs. Then I am going to use the SATADOM for CentOS 7 KVM install. This way I can simply change the boot device to finish the process once iRedmail release for CentOS 7 is available. Thanks again!

aks
Posts: 3008
Joined: 2014/09/20 11:22:14

Re: Best Practice KVM LVM SSD SAS SATA Config

Post by aks » 2014/12/30 13:04:45

To be hopest, there are no "best practice" when it comes to storage. The best thing you can do is layout the disks so the application(s) get the best disks (in terms of realibility and performance). Personally, I'd keep swap off the SSD (doe to potential wear problems) and perhaps use some of the SSD as a cache for the SAS and/or SATA disks.
The disk alignment problem can be a big problem as you scale up. Google for it, there's a lot of information out there about it. Sorting that out sooner rather than later will make your life easier (just an opinion).

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