[Beowulf] hardware RAID versus mdadm versus LVM-striping

Gerald Creager gerry.creager at tamu.edu
Sun Jan 17 23:54:52 EST 2010


+1: Reality.

Joe Landman wrote:
> Rahul Nabar wrote:
>> On Sun, Jan 17, 2010 at 9:36 PM, Joe Landman
>> <landman at scalableinformatics.com> wrote:
>>> Ohhh ... it depends.  Some of the "vendors" hardware raid ... heck 
>>> ... most
>>> of it ... is rebadged LSI gear.  Usually their lower end stuff which is
>>> sometimes fake-raid.  Use fake-raid only if no other options exist.
>>
>> Thanks Joe! What's "fake RAID"? Just a bad implementation or...........?
> 
> Its a software RAID implementation pretending to be a hardware RAID 
> implementation.  They are rarely if ever as good as MD.  Many of them in 
> Linux will invoke dm (the "other" RAID engine) as dm has "support" for 
> fake-raid.  Note that we have lost data (multiple times) with 
> dm+fake-raid in testing, so we don't recommend its use in important 
> machines (ones which you can't afford to lose).  This could be due to 
> bad drivers for the chips in question, but we aren't taking chances.
> 
>>
>>
>>> LVM is not a performance tool.  Use it to help you manage things, not 
>>> speed
>>> things.
>>
>> I had thought so. But why then does LVM have features like striping if
>> not for performance? Or are they just not so good?
> 
> LVM doesn't perform as well as MD RAID for performance.  You can use it, 
> just be advised that you are leaving a great deal of performance on the 
> table if you do so.
> 
> 
>>
> 
> 

-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843
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