virtualization - What are the benefits of having local disks on hypervisor nodes running VMs off a SAN?

When an hypervisor like XenServer or vSphere can be run on diskless nodes (eg. by booting from flash cards or from the network) and VM storage is handled via a SAN, is there any good use for local disks?

Would it be better to have those disks even if not used to boot the hypervisor or to hold VMs?
What are the reasons, if any, to choose completely diskless servers VS having some local storage?

Answer

I don't have a ton of XenServer experience, but here's some information coming from a VMware background.

vSphere ESXi runs completely in memory following boot, so local storage JUST for the ESXi installation is generally considered overkill. Booting off SD card/USB stick/PXE(network) is supported under ESXi, so there's lots of options.

Servers with no local storage have some benefits, primarily:

Lower cost

Lower power consumption

Less heat generated by server

However, this doesn't mean local storage can't be useful. First and foremost, you can configure ESXi to use local storage for VM swapfiles. This reduces load on your SAN and can improve performance under some workloads. Since these swapfiles are small in size, and temporary in nature, you can use small (70GB-150GB) 15k RPM SAS drives to get good performance for a low price.

Also, new in ESXi 5.5 is Flash Caching, which allows you to use SSDs local to the ESXi host to intelligently cache VM data. This reduces load on the SAN and improves performance for those VMs. This isn't cheap, but it can speed up some workloads significantly.

So, hypervisor configurations with local disk can be "better" if your workload can capitalize on localized swapfiles or Flash Caching. If you don't think those features will help you, than there's no compelling reason to use local disk.

Comments

linux - iDRAC6 Virtual Media native library cannot be loaded

When attempting to mount Virtual Media on a iDRAC6 IP KVM session I get the following error: I'm using Ubuntu 9.04 and: $ javaws -version Java(TM) Web Start 1.6.0_16 $ uname -a Linux aud22419-linux 2.6.28-15-generic #51-Ubuntu SMP Mon Aug 31 13:39:06 UTC 2009 x86_64 GNU/Linux $ firefox -version Mozilla Firefox 3.0.14, Copyright (c) 1998 - 2009 mozilla.org On Windows + IE it (unsurprisingly) works. I've just gotten off the phone with the Dell tech support and I was told it is known to work on Linux + Firefox, albeit Ubuntu is not supported (by Dell, that is). Has anyone out there managed to mount virtual media in the same scenario?

hp proliant - Smart Array P822 with HBA Mode?

We get an HP DL360 G8 with an Smart Array P822 controller. On that controller will come a HP StorageWorks D2700 . Does anybody know, that it is possible to run the Smart Array P822 in HBA mode? I found only information about the P410i, who can run HBA. If this is not supported, what you think about the LSI 9207-8e controller? Will this fit good in that setup? The Hardware we get is used but all original from HP. The StorageWorks has 25 x 900 GB SAS 10K disks. Because the disks are not new I would like to use only 22 for raid6, and the rest for spare (I need to see if the disk count is optimal or not for zfs). It would be nice if I'm not stick to SAS in future. As OS I would like to install debian stretch with zfs 0.71 as file system and software raid. I have see that hp has an page for debian to. I would like to use hba mode because it is recommend, that zfs know at most as possible about the disk, and I'm independent from the raid controller. For us zfs have many benefits, ...

linux - Awstats - outputting stats for merged Access_logs only producing stats for one server's log

I've been attempting this for two weeks and I've accessed countless number of sites on this issue and it seems there is something I'm not getting here and I'm at a lost. I manged to figure out how to merge logs from two servers together. (Taking care to only merge the matching domains together) The logs from the first server span from 15 Dec 2012 to 8 April 2014 The logs from the second server span from 2 Mar 2014 to 9 April 2014 I was able to successfully merge them using the logresolvemerge.pl script simply enermerating each log and > out_putting_it_to_file Looking at the two logs from each server the format seems exactly the same. The problem I'm having is producing the stats page for the logs. The command I've boiled it down to is /usr/share/awstats/tools/awstats_buildstaticpages.pl -configdir=/home/User/Documents/conf/ -config=example.com awstatsprog=/usr/share/awstats/wwwroot/cgi-bin/awstats.pl dir=/home/User/Documents/parced -month=all -year=all...

Blog

Search This Blog