[Samba] suggestions for a "fast" fileserver - 1G / 10G

[Christopher Chan]

On Tuesday, March 25, 2014 04:56 PM, Emmanuel Florac wrote:
> Le Mon, 24 Mar 2014 21:55:57 -0700 vous écriviez:
>
>
>> -----
>> Note, I found your info excellent.  But had some Q's
>> ----
>> Well a partial quote from one of the fs experts on the xfs
>> list:
>>
>>   From the above, I don't see how RAID6 could be faster than RAID0
>> unless you are exceeding the card capacity (3.0Gb/s or 6.Gb/ or 12...
>> depending on SAS generation).
> I suppose you mean "faster than RAID-10" here; RAID-6 is of course
> never faster than RAID-0, at best just as fast (usually slightly worse
> or less). RAID-10 write throughput is half the total write throughput
> of your disks, i. e. if you have 12 drives able of 100 MB/s each, your
> top sequentially write speed is 600 MB/. Same goes for top sequential
> read, though theoretically it should be possible to use alternate disks
> from the mirrors to actually read at full speed (1.2 GB/s); however it
> doesn't seem to be the case in most RAID-10 implementations I've looked
> at.
>
> On the other hand a RAID-6 with the same exact 12 drives is able to do
> 1 GB/s writes (10 x 100MB/s) and 1.2 GB/s reads provided that the
> controller is able to compute parities fast enough.
and have sufficient cache.

>
> In the case you're mentioning it seems that the problem is with
> rewrites. As I wrote in my previous message, rewriting a single block
> (not a full stripe) in RAID-6 actually requires 3 single disks reads
> and 3 writes, severely impacting performance.
hence a large cache. The writes can wait.