[mythtv-users] Where are those new 1TB drives?

jedi at mishnet.org jedi at mishnet.org
Mon Mar 12 14:14:20 UTC 2007

> On Sunday 11 March 2007 23:09, Dan Ritter wrote:
>> On Sat, Mar 10, 2007 at 05:23:30PM -0700, Brian Wood wrote:
>> > RAID5 is a good compromise between redundancy and capacity. It does
>> > have a bit more overhead than RAID0 or RAID1 but that's really not a
>> > problem with any machine made in the last decade. You need a minimum
>> > of 3 same-size drives (or at least same-size partitions), so with the
>> > drives you describe you would use both 250s and a 250GB partition on
>> > the 350 for a total of 500GB storage. That leaves some left on the
>> > 350 for an operating system, swap, and possibly a boot partition.
>> Myth users generally like RAID 5 because:
>> - it's relatively cheap. You lose the capacity of 1 drive in N,
>>   usually 1/4 or 1/5.
>> - the data is not very expensive (record another showing)
>> - the data is not very expensive (rip it off the DVD again)
>> - the data is not very expensive (no one is paying you to do
>>   this)
>> For many applications, though, RAID 5 is a bad idea.
> All the RAID talk on this list is fun to read.
> But "real" enterprices raid systems are using battey backed-up read and
> write
> caches.  And ones you have these, the raid level doesn't matter anymore.
> Performance is allmost the same for all raid levels, so raid5 is the best
> choice because of the cache.

    That's a very dangerous assumption. It's rediculously easy to
overwhelm the RAM cache on even the most expensive SAN hardware.

> Do you know that they changed the cache algorthm some time ago so you get
> the
> _same_ performance with _halve_ the cache size ?
> Mhh, I like 4gbit fiber attached 15k fiber disks and 4 GB battery cache
> .....


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