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From:Johan De Meersman Date:March 16 2011 7:42am
Subject:Re: Suggestions for InnoDB files
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> From: "Adarsh Sharma" <adarsh.sharma@stripped>
> Johan De Meersman wrote:
> > Interesting, but why like this instead of simply larger disks or raidsets ?
> It's the IT-Admin Issue , I can't question that and we have only disks of 300GB ( SAS
> ).

Your admin is supposed to provide services that benefit the application you need to run on
the server. You're stuck with the hardware, but not the setup.

> > Why would you use 8G datafiles instead of large, partition-filling ones?
> What is your recommendations for number of ibdata files , keeping in Mind Raid10 is
> not used and the size of tables .
> Because in RAID10 :
> We can utilize 50 – 55 percent size of hard disk.(50-55 % of 4 hard disk total
> space if hard disks are 500 GB X 4 then we can 
> utilize only 1 TB space from 2 TB.

Correct. That's the price you pay for the performance and redundancy RAID10 gives you.
Nothing is free in life :-) Incidentally, it's going to be exactly 50% - I'll be very
interested to see where he pulls those extra 5% from.

You could ostensibly go for RAID5, which will allow you to use 1.5 TB off those same four
disks, at a minor loss of disk redundancy (only one may fail) and some loss of performance
- but still better than no RAID at all. If you want to lose no space at all, use RAID0
(striping) to increase performance, but that offers no disk redundancy at all - single
disk fails, you lose all data.

As a small overview, RAID 10 gives you the benefits of striping (data for a single file is
split over multiple disks) so reads and writes faster, AND of mirrorring (every block is
available on multiple disks, which provides insurance data loss when a disk breaks and
additionally increases the read speed even more. You won't actually quadruple the read
speed, but I wouldn't be surprised to see it triple on a 4-disk RAID 10.

RAID 5 uses one of your disks for redundancy purposes, so any single disk may fail and
you'll still have all your data. Data is striped, so disk performance also increases,
although not as much as mirrorring. This is however the most CPU-intensive form, as
checksumming over all disks happens at every write. This also makes that write speed won't
see as much benefit.

RAID 0 has no redundancy whatsoever - if anything you could say it's worse than data over
multiple disks, because if one disk fails the entire volume is lost. Because it offers
striping, however, it gives performance a good boost.

> Software RAID is not reliable on production environment because software raid is
> dependent on hardware and software both thing 
> if one thing go down then it will not work, but in hardware raid there is no role of
> software every thing is depend on hardware.
> But, We are not able to afford Hardware RAID.

Maybe you shouldn't have an OS then, either; because if that fails everything is down? My
word, if that's his excuse, I seriously recommend you get a better admin.

Software RAID offers the same or better performance than hardware RAID, save for the real
high-end RAID cards. Additionally it offers more flexibility in the setup - many
combinations of RAID levels are possible, whereas the majority of controllers offer 1, 5
and 10 at most.

An additional benefit that is not to be laughed at, especially if you're on a budget, is
that software RAID will work regardless of the hardware involved. Hardware RAID
controllers tend to have their own specific set of metadata on the disks, and if your
controller breaks, you had better manage to get the exact same one, or you risk not being
able to read your disks. Sofware RAID, by virtue of being software, can simply be
reinstalled on another system if need be. Tell MD to scan for and assemble RAID arrays and
it'll just find the appropriate partitions and match the pieces together. No more
accidentally putting a disk in the wrong bay and having it break the RAIDset. (I'll admit
that has become rare with controllers getting smarter over the years, but I've seen
multi-terabyte arrays go useless because some idiot operator switched two disks into the
wrong bays)

So, yes, my recommendation remains the same: switch the system to software RAID;
preferably 10, 5 or 0 if you really need all that space.

Bier met grenadyn
Is als mosterd by den wyn
Sy die't drinkt, is eene kwezel
Hy die't drinkt, is ras een ezel
Suggestions for InnoDB filesAdarsh Sharma16 Mar
  • Re: Suggestions for InnoDB filesJohan De Meersman16 Mar
Re: Suggestions for InnoDB filesJohan De Meersman16 Mar
  • Re: Suggestions for InnoDB filesAdarsh Sharma16 Mar
    • Re: Suggestions for InnoDB filesJohan De Meersman16 Mar
    • RE: Suggestions for InnoDB filesRolando Edwards16 Mar