Stripe sizes with gstripe

[David Kelly]

On Jun 12, 2008, at 3:21 PM, Kirk Strauser wrote:

> Does gstripe read an entire stripe at a time?  If so, why do that  
> instead of
> just reading a few requested blocks?  If not, then is there any  
> advantage
> to large stripes?

Apparently it won't read anything larger than your stripe size which  
defaults to a miserable 4k.

Doesn't appear the driver collects multiple pending reads and merges  
them into one transaction. Don't know if ATA/SATA allows that or not,  
believe it was called "scatter/gather" in SCSI.

Built a gstripe volume a while back and played with various stripe  
sizes trying to maximize KB/t as shown in "systat -v" during massive  
file read/writes. A stripe size of 131072 (128k bytes) was the best I  
could get at about 43 KB/t. About 25 MB/sec each on two drives that  
are capable of 4x that on a Mac Pro (about 55 MB/sec single drive on  
inner tracks to 100 MB/sec on outer, reading with md5).

Anyway, throughput was terrible with the default 4k stripe.

If there is a tuning knob that I have missed, would appreciate being  
told what.

IIRC vinum's default stripe was about 87.5kB and "systat -v" reported  
transactions of that size.

--
David Kelly N4HHE, dkelly at HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.