Re: access to hard drives is "blocked" by writes to a flash driv

Content-Type: text/plain; charset=ISO-8859-1
--------
In message <1362317291.1195.216.camel@revolution.hippie.lan>, Ian Lepore writes
:

>I run into this behavior all the time too, mostly on arm systems that
>have an sd card or usb thumb driver as their main/only drive.

This is really a FAQ and I belive I have answered it N times already:

There are, broadly speaking, two classes of flash-storage: "Camera-grade"
and "the real thing".

"Camera-grade" have a very limited "Flash adaptation layer" which typically
only can hold one flash-block open for writing at a time, and is typically
found in CF and SD cards, USB sticks etc.

Some of them gets further upset if the filesystem is not the FAT they
expect, because they implement "M-Systems" (patented) trick with monitoring
block deletes in FAT to simulate a TRIM facility.

A number of products exist with such designs, typically a CF-style, is
put behind a SATA-PATA bridge and sold as 2.5" SSD SATA devices.
"Transcend" have done this for instance.

If you use this class of devices for anything real, gstat will show
you I/O write-times of several seconds in periodic pile-ups, even
100 seconds if you are doing something heavy.

For various reasons (see: Lemming-syncer) FreeBSD will block all I/O
traffic to other disks too, when these pileups gets too bad.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.
_______________________________________________
freebsd-current@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-current
To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"