[kwlug-disc] [OT] linux server power

John Van Ostrand john at netdirect.ca
Mon Jan 31 10:36:04 EST 2011


----- Original Message -----
> No offense, but this is *scary*? Where did you find such
> misinformation?
> SSDs are in every way faster than HDD: faster seek times, faster
> throughput. I can't think of any reason why using an SSD would make
> VoIP performance suffer over an HDD.

SSD performance depends on a few factors and SSDs can be slower in re-write speeds. On certain workloads the slower re-writes can offset the read gains of SSDs. 

When overwriting blocks on an SSD the block must first be erased so essentially a re-write is a read-erase-write process. Additionally SSDs store information in blocks larger than 512 bytes (4 KiB I think.) And so a file system that is not perfectly aligned to the 4 KB will require two read-erase-write operations.

Conventionally disks have had no way of knowing if a block is still in use because disk drivers don't understand file systems and file systems haven't expected disks to care. TRIM is a way to correct that and tell the drive that a block is unused so it can be erased at it's leisure removing the "erase" step when writing to unallocated, but previously used blocks.

Is there an implementation for TRIM in linux now? That would increase performance.

-- 
John Van Ostrand 
CTO, co-CEO 
Net Direct Inc. 
564 Weber St. N. Unit 12, Waterloo, ON N2L 5C6 
Ph: 866-883-1172 x5102 
Fx: 519-883-8533 

Linux Solutions / IBM Hardware 




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