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xen-users
RE: [Xen-users] How many guests
Hi Michael,
Do you have any links to any of those devices you mentioned?
Also, would using a software iSCSI initiator defeat the purpose of
using RAID10 for performance?
Thanks
From: Michael Schmidt
[mailto:michael.schmidt@xxxxxxxxxx]
Sent: Mon 07/06/2010
08:53
To: Jonathan Tripathy
Cc:
Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] How many
guests
Hi Jonathan,
for iSCSI a iSCSI storage is suggestable, or
opene if you plan to run it
on a x86 server.
But you need dedicated lan
line, a storage box with its own raid
controller and cpu, memory and so
on.
And a iSCSI hostbus adapter (around 600€) on the xen host side. If
you
dont have a iSCSI HBA, you have to use the
software iSCSI initiator (i
dont like this piece of software, and you
have iSCSI CPU Usage on your
host).
If you want to run just a few more disks for one server (without
HA
options), you dont need all this overhead.
Buy additional to your xen
host a SAS Raid controller with an external
port (+150€). And a 12-disk JBOD
(800€) and the disks (SATA / SAS).
This provides you a lower TCO and a
higher energy efficiency (3-4U and
450W for 60 VMs).
Best
Regards
Michael Schmidt
Am 07.06.10 09:16, schrieb Jonathan
Tripathy:
> Hi Michael,
>
> You state that iSCSI is reliable
but expensive. But isn't iSCSI nearly
> free?
>
> I agree with
you that Fibre Channel systems are very expensive
>
> Would iSCSI
over IP be ok?
>
> Thanks
>
>
> On 07/06/10 08:12,
Michael Schmidt wrote:
>> This is not completely correct.
>>
With a raid 1, you have the read performance of 2 disks and just the
>>
write performance of a single disk.
>>
>> To the other thinks
following this thread:
>> If you use a network storage, you have a
bandwidth limit with the
>> connection. But in the most cases, the raw
bandwidth is not the
>> bottleneck (instead of the IOs per
second).
>>
>> Network Storages using NFS or NBD are not
stable enough in my eyes.
>> iSCSI and FC SANs but really stable and
expansive as well. But there
>> is another much less expensive
way:
>>
>> You get the most servers with an external SAS port.
There you can
>> connect over a SAS link a JBOD with 12 - 16 disk bays
(DAS).
>> This disks can be managed by the servers raid
controller.
>>
>> Best Regards
>>
>> Michael
Schmidt
>>
>>
>> Am 06.06.10 23:21, schrieb Bart
Coninckx:
>>> RAID1 does not perform better than a single disk. It
will still
>>> depend on what
>>> those 5 to 10 VMs
would do. It still might be stretching it. For 10
>>>
webservers
>>> visited by 5 users per hour: I would say no problem.
For 5 heavily used
>>> database servers it will be another
story.
>>>
>>> I guess the only real way to find out is
to put your guests on there
>>> and try.
>>> If you
clone them, you will know quite
fast.
>>>
>>>
>>> On Sunday 06 June 2010
21:38:54 Jonathan Tripathy wrote:
>>>> Thanks
Micael,
>>>>
>>>> I understand what you are
saying.
>>>>
>>>> With a small setup such as a
RAID1 array, how many VMs could I rent
>>>>
out?
>>>>
>>>> It doesn't matter if it's a small
number, it's just to utilise the
>>>> server a
bit.
>>>>
>>>> Think it would cope with
5-10?
>>>>
>>>>
Thanks
>>>>
>>>>
Jonathan
>>>>
>>>> On 06/06/10 20:18, Michael
Schmidt wrote:
>>>>> Hi
Jonathan,
>>>>>
>>>>> if you plan to migrate
existing physical machines to xen VMs, or you
>>>>> have some
different machines for a comparison,
>>>>> you can easy get
runtime statistics and calculate the usage. Look at
>>>>> the
running iostats and cpu usage.
>>>>>
>>>>>
If you plan to rent generic VMs on this server to customers, you
disk
>>>>> / raid setup will be absolutely the
bottleneck.
>>>>> A solution at this point is not easy. If you
have much write IOs, use
>>>>> raid 10 with 4 to 8 disks. With
many reads - raid 6 or 50 with the
>>>>> same amount of
disks.
>>>>> In each case i can suggest you 15k rpm SAS
disks.
>>>>>
>>>>> Then you can run 29 VMs.
Or 60 VMs with 16GB memory and 2
CPUs.
>>>>>
>>>>> But note: You cannot set
disk priority to the VMs. So if one VM does
>>>>> heavy disk
IO, all off the other VMs slowed
down.
>>>>>
>>>>> Best
Regards
>>>>>
>>>>> Michael
Schmidt
>>>>>
>>>>> Am 06.06.10 20:45,
schrieb Jonathan Tripathy:
>>>>>> Hi
Michael,
>>>>>>
>>>>>> Thanks for your
email.
>>>>>>
>>>>>> This is just an
idea that I have floating around in my head that
>>>>>>
maybe I'd like to rent out some VPSs to customers, just
to
>>>>>> utilise my
>>>>>> machine
which will be sitting in a co-lo nearly
idle.
>>>>>>
>>>>>> I'd give out VPSs
with 256MB RAM and probably 5Mbps connection
>>>>>>
speed.
>>>>>>
>>>>>> So the answer is,
I don't know what will be running on them, however
>>>>>> I
could write up an "acceptable use policy", as well as use
some
>>>>>>
throttling/scheduling?
>>>>>>
>>>>>>
Thanks
>>>>>>
>>>>>> On 06/06/10
19:39, Michael Schmidt wrote:
>>>>>>> Hi
Jonathan,
>>>>>>>
>>>>>>> the
question is, what a kind of VM?
>>>>>>> You can
over-utilize a much greater machine with one VM.
>>>>>>>
Or on the other side, you can run 40 VMs on a shorter
machine.
>>>>>>>
>>>>>>> Each
ressource can be a
bottleneck
>>>>>>>
>>>>>>> -
Memory - this is realy easy to calculate: Avaiable minus
768MB
>>>>>>> (Reserved for Dom0 should be enugh in this
case).
>>>>>>> - CPU - Here we need a VM
statistic
>>>>>>> - Disk Bandwidth - Here we need a VM
statistic, but in the most
>>>>>>> cases not the
bottleneck
>>>>>>> - Disk IOPS - Here we need a VM
statistic, in the most cases the
>>>>>>>
botelneck
>>>>>>>
>>>>>>> What a
kind of VMs you plane to run?
>>>>>>> Webservers /
mailservers / database-servers
...?
>>>>>>>
>>>>>>> Best
Regards
>>>>>>>
>>>>>>> Michael
Schmidt
>>>>>>>
>>>>>>> Am
06.06.10 00:54, schrieb Jonathan Tripathy:
>>>>>>>>
Hi
Everyone,
>>>>>>>>
>>>>>>>>
I have a Dell R210 server which has a Xeon X3430 Quad Core
CPU
>>>>>>>> (2.4Ghz x 4) with 8GB of RAM. I intend
to use the H200 controller
>>>>>>>> in a RAID1
setup
>>>>>>>>
>>>>>>>>
How many VMs do you think I'd be able to run on this
machine?
>>>>>>>> Is
20
>>>>>>>> pushing
it?
>>>>>>>>
>>>>>>>> I'd
say most (if not all) guests would be in PV
mode.
>>>>>>>>
>>>>>>>>
Thanks
>>>>>>>>
>>>>>>>>
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>>>>>>
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