Re: AWS EC2: Debian 7.4 AMIs now available
On Mon, Feb 10, 2014 at 2:38 AM, Alistair Prestidge
<alistair.prestidge@googlemail.com> wrote:
> Hi brain thanks for your reply.
>
> You say in almost all cases you would recommend esb backed device's. Can I
> ask why? Iam looking to migrate to instance store from ebs mainly for io
> reliability issues.
>
> I am having io issues with ebs backed instances the io can be very erratic
> and cause my sites to have very slow response times from time to time.
>
> I have currently put the code and logs on an ephemeral partition and the
> sites are much more stable.
>
> I have no reason to keep any code or data that is on the server after reboot
> or termination.
>
> Thanks
Well you may actually have a use case that justifies instance-store,
if cost is a
big concern. Typically I have found EBS more pragmatic for the
following reasons:
1) Can base infrastructure off of a single AMI, and use Block Device
parameters [1]
to change the characteristics of the resulting root volume. (i.e.
- one can specify
block device size and performance characteristics.)
2) One is not limited to a 10GB root volume. (1TB is EBS current limit.)
3) In the case one needs variant AMIs, it is generally much simpler
with EBS root
volumes, since the process is "snapshot" based, and controllable
at the API layer.
4) One gets many of the benefits of a Storage Area Network, at
reasonable prices.
(Snapshots, volume cloning, etc.)
5) Allows me to prototype on t1.micros, which don't support instance
storage, and
bring them up as a different instance type for production.
6) Data persistence in the face of HW failure.
I like you have also observed that an instance-store root volume has
more consistent
performance than a standard EBS volume. However, the introduction of Provisioned
IOPS [2] EBS volumes has largely changed this for root volumes, as I
can now crank up
the disk performance, but it can get expensive. (Basically you can pay
extra and get an
SLA on your disk performance).
Also do be aware that EBS volumes have a first-access penalty, that
can be addressed
by prewarming your volume. [3]
Bear in mind you can use an EBS root volume, and still take advantage
of instance-
storage for non-root partitions. (For all instance types except
t1.micros, which come with
no instance storage.)
Currently I believe the best deal on AWS instances for smallish fast
storage, might be the m3
class of instances, where one of the ephemeral (instance-store) block
devices is backed by
local SSD. [4] (Whether instance-store or EBS root)
Cheers,
Brian
[1] - http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-device-mapping-concepts.html
[2] - http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-io-characteristics.html
[3] - http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-prewarm.html
[4] - http://aws.typepad.com/aws/2014/01/aws-update-new-m3-features-reduced-ebs-prices-reduced-s3-prices.html
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