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From: Aaron Blew (aaronblewgmail.com)
Date: Fri Sep 26 2008 - 01:54:55 CDT
Overall and most of the time, SANs are a good thing. They have several
advantaged over dedicated directly attached storage arrays:
1.) They're generally a lot smarter about how and when they write and read
to the disks. Often they understand what's going on down at the head level,
and can leverage that for better performance.
2.) They've generally got a lot more cache than a directly attached array
(some systems can have up to 256GB of cache)
3.) They're a lot more reliable than many direct attached arrays. There
have been many many hours put into algorithms to detect and predict disk
failures by these SAN vendors, and they're designed to keep that data online
as much as possible as their reputation rides on their availabity. Hitachi
Data Systems (as one example) even offers configurations with a 100% data
availability guarantee (so long as the unit has power)
4.) Having all those spindles under one management/virtualization framework
makes you a lot more agile with how you can make use of your storage. The
MySQL workloads your environment has may not all be striped across all the
spindles within the SANs, segregating the workloads. However, using all the
spindles available can have advantages in some workloads as well, since not
all databases will be hammering down to the spindle all the time.
A SAN environment isn't always a trivial thing to operate, but it will save
a lot of time over managing 100s of direct attached arrays and can offer
performance capabilities way beyond what can be practically achieved by
using direct attached storage.
On Thu, Sep 25, 2008 at 6:38 PM, Michael Dykman <mdykmangmail.com> wrote:
> Hello all,
> I recent started employment with a company which has a lot of mysql
> servers (100+ is my best estimate so far) and have all of their
> database servers, masters and slaves alike, using one of 2 SANs for
> data storage. They servers are connected to dedicated switches with
> fibre to to SANs and the SANs themselves seem to be well configured
> and tuned.
> However, it seems preposterous to me that all those very busy
> databases should, by design, have a common bottleneck and share a
> single point of failure. I am not deeply knowledgeable about SANs or
> their performance characteristics; my reaction thus far is pretty much
> intuition but I help can't but picture the simple analogue of single
> disk or a RAID 10 with synchronized spindles frantically thrashing
> back and forth to respond to tens of thousands of queries per second.
> Would anyone care to comment? Is my concern justified or am I merely
> - michael dykman
> - mdykmangmail.com
> - All models are wrong. Some models are useful.
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