[Tig] St. Diig

[Bob Friesenhahn]

On Thu, 18 Oct 2007, timothy norman huber wrote:
>
> We're working on the I/O bottleneck at Violin.
>
> Right now we've got 1/2 TB of DRAM in 2U connecting via PCIe.

Speaking of I/O bottleneck, since DRAM is volatile, how long does it 
take to load data into that 1/2 TB of DRAM from traditional disk or 
tape so that actual work can be started?  How long does it take to 
copy the finished work from 1/2 TB of DRAM to backing disk?

FLASH devices are non-volatile but they also tend to wear out after 
many repeated writes, which is a common pattern in some usage models. 
That is not to say that hard drives don't wear out, but their failure 
mechanisms are different and time to fail is not really coupled to the 
amount of accesses.

How many times may the type of FLASH memory used for such large 
storage be repeatedly written before failures start to occur?

What is the MTBF per field replaceable component, MTBF for a full 2U 
unit, and how difficult is the device to repair?  Can the device 
continue operating while a failing component is replaced?

It is interesting that filesystem design has a quite a lot to do with 
how many writes occur per sector.  A copy-on-write filesystem like 
Sun's ZFS is going to write each location on disk less often than a 
filesystem which updates by overwriting existing data.  Some 
filesystems put their "FAT" or superblocks at fixed locations so they 
will wear out those areas much faster.

> Random I/O kills even the fastest HDD technology.  15k drives have

This is definitely true, but most post-production/DI tasks do hardly 
any random I/O at all.  Most accesses are sequential and use the full 
block size.  Sequential throughput drives performance for DI work.

Random I/O performance is vital for database storage.

Bob
======================================
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/