
RAID 0 on EC2 EBS volumes using mdadm  - mcxx
http://groups.google.com/group/ec2ubuntu/web/raid-0-on-ec2-ebs-volumes-elastic-block-store-using-mdadm?pli=1
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seiji
Nice disclaimer: "Beware: 40TB of EBS storage will cost $4,000 per month plus
usage charges."

I'd rather see it tried with ZFS and RAID-Z.

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mdasen
So, RAID-Z is awesome, but probably not so useful in this case.

RAID-Z, among other things, is designed to offer parity (in a better
implementation than traditional RAID parity). But you probably don't care
about that with EBS. EBS volumes have an annual failure rate of 0.1%-0.5%.
Commodity disks have an annual failure rate of 4%. That means that EBS is
already taking care of parity in some way and you probably should worry about
things other than that - like speed.

So, you could use RAID-Z to increase reliability (and it's a wonderful
technology), but the speed of RAID-0 would be really nice for a good database
server given that parity is taken care of.

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dcurtis
I was under the impression that S3 data, including EBS, has never had a case
of data loss that Amazon knows of.

Where did you get your annual failure rate data?

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mdasen
<http://aws.amazon.com/ebs/>

There's a section called "Amazon EBS Volume Durability" that goes over it. S3
is different from EBS. S3 is a lot more reliable. S3 is a spray files all over
the place system like Danga's MogileFS. You simply save, say, 5 copies of a
file on random servers and the likelihood that you're going to have data loss
on all 5 of those servers before the system can replicate back up to having 5
copies of the file is next to nothing. Like, you loose two copies, but then
the system creates two new copies on two other servers to get back up to 5
copies of the file.

EBS is less reliable. It's more like a RAID array. You can't really have a
volume that spans different machines, nevermind a volume that spans data
centers as S3 can. With EBS, a fire could just burn the disks an that would be
the end of it (while, with S3, other data centers are unlikely to experience a
similar fire in a short time frame). It's highly unlikely that EBS will fail
on you - with an annual failure rate of 0.1%-0.5%, you shouldn't have to worry
much.

So, EBS is a reliable storage system, but it isn't S3. Of course, S3 could
never be fast like EBS. So, there is a trade off. Really, with EBS you can
just snapshot it to S3 ever day and sleep soundly. In the highly unlikely
event that you have a failure, you can restore without loosing more than 24
hours of data and the chance that you'll have to even do that is so low, but
not as low as S3 where you can sleep completely soundly.

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dcurtis
Ah, that makes sense. I'm not sure why I thought EBS was stored on S3. Thanks
for the detail.

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danw
EBS snapshots are stored on S3, which you can restore from if you lose the EBS

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skorgu
This is a crime against god and man and I love every second of it.

