On 5/11/18 8:20 am, Wol's lists wrote:
On 31/10/2018 12:12, Adam Goryachev wrote:
We won't have 10G ethernet here, just a single 1G ethernet. It is
only our DR system, so crappy performance is not an issue for a few
days or so while we source better/faster equipment to get back to a
fully working/functional system.
Thank you for your reply, you do a lot of great work on this list ;)
Let me get this right. You're buying expensive SSDs to populate a DR
system? Is that really a good idea?
Nope, sorry, that wasn't what I said (or at least, not what I meant).
We need additional capacity for our primary SAN, so we are replacing
both the primary and secondary san ssd's (each has 8 x 800GB SSD), with
new 1.9T ssd's (5 in each). Therefore, we will have 16 x 800G ssd's
spare from the 2 old servers.
I don't know the figures, but how many rotating rust disks would you
need in a raid 6 to be able to read fast enough to saturate a 1G
ethernet? Then look at how much of that workload is streaming new data
to write, and how much is a dataset being actively modified?
The problem is that the workload is small random IO. (ie, multiple
windows VM's doing SQL server, terminal server, mail server, etc tasks).
We have tried rust previously on the live servers, and rapidly upgraded,
currently, even the primary servers with all SSD's can get behind at times.
I don't know what state it's in, but there's also the journal work
that was meant, among other things, to "close the raid 5 write hole",
but part of the idea behind that was also to enable sticking an SSD
cache in front of a rotating disk back end to speed up the array.
I'm not ready to deploy new technology like this yet... The point of the
DR is to be 100% it will work when we need it (ie, we are already in the
middle of a disaster, potentially without me or anyone else sufficiently
technical to work through whatever minor issues crop up when you least
expect it).
It looks to me like your ethernet is already the bottleneck, and
worrying about the disks is addressing completely the wrong problem.
TBH, I'm not that concerned about performance for the DR, but since we
have the SSD's available/spare, it would be a waste not to use them. The
alternative would be to sell them, but I'm not sure we would get
sufficient money back, thus it's better to just re-task them instead.
Regards,
Adam
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Adam Goryachev Website Managers www.websitemanagers.com.au
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