What is the difference between ramdisk created using Efsys.ram and ramdisk
created by Fsys
Which is efficient?
On 26 May 2004 12:04:41 GMT, Erick Muis <emuis@node55.ott.qnx.com> wrote:
Unless you have a reason to use Efsys.ram, it is generally best to just
go with the Fsys based ramdisk.
There is yet another utility to have a ram-disk: /bin/vdir
If one compares three of them Efsys.ram, vdir and Fsys based ramdisk, what
are pros and cons?
Tony.
Efsys.ram uses the embedded flash filesystem, whereas the ramdisk created by
Fsys uses a traditional block filesystem. The Fsys based ramdisk will be
faster, as it doesn’t have reclaim, and other flash filesystem overhead.
Unless you have a reason to use Efsys.ram, it is generally best to just go
with the Fsys based ramdisk.
Best regards,
Erick
viswanathan <viswanathan.kl@geind.ge.com> wrote:
What is the difference between ramdisk created using Efsys.ram and ramdisk
created by FsysWhich is efficient?
–
Erick Muis
Hardware Group
QNX Software Systems Ltd.
Email: emuis at qnx.com
Hi Tony,
Forgot about vdir, the nice thing about vdir is that it reclaims memory,
and allocates memory as needed, so it is a bit more dynamic. That being
said, I don’t know the internals of how it works specificly, however the
ability to allocate and reclaim memory dynamicly does sound rather nice,
compared to the static sizes given by Efsys.ram and Fsys. However I am
sure that those also come with a cost of having to allocate that memory
and free it.
Really if you don’t need an embedded flash filesystem there is no point to
running Efsys.ram. So really the comparison should be between vdir and
the Fsys based ramdisk.
I think I covered the pros/cons for vdir above, so for the Fsys based one
(although others may be able to provide further detail). I would say that
Fsys would be faster based upon the fact that it would allocate a static
sized disk, and it wouldn’t have to free and allocate when more is needed.
Also with a Fsys based ramdisk you don’t need to worry about not having
enough memory if there is a bunch of applications running. You will know
how much you have and how much you will have left at all times.
Regards,
Erick
Tony <mts.spb.suxx@mail.ru> wrote:
On 26 May 2004 12:04:41 GMT, Erick Muis <> emuis@node55.ott.qnx.com> > wrote:
Unless you have a reason to use Efsys.ram, it is generally best to just
go with the Fsys based ramdisk.
There is yet another utility to have a ram-disk: /bin/vdir
If one compares three of them Efsys.ram, vdir and Fsys based ramdisk, what
are pros and cons?Tony.
–
Erick Muis
Hardware Group
QNX Software Systems Ltd.
Email: emuis at qnx.com
Mario Charest postmaster@127.0.0.1 wrote:
With Fsys the drawback is the ram disk share the cache with the HD.
No. The ramdisk resides in its own ram area (equal in size to -r
value) and independant of Fsys buffer cache area (-c value). Access
to the ramdisk does not go through this cache.
As has been pointed up, you do have to specify the complete size to
set aside for the ramdisk when you start it, after which this does
not change and is effectively treated as a disk of that size.
“Erick Muis” <emuis@node55.ott.qnx.com> wrote in message
news:c92i2n$85b$1@inn.qnx.com…
Hi Tony,
Forgot about vdir, the nice thing about vdir is that it reclaims memory,
and allocates memory as needed, so it is a bit more dynamic. That being
said, I don’t know the internals of how it works specificly, however the
ability to allocate and reclaim memory dynamicly does sound rather nice,
compared to the static sizes given by Efsys.ram and Fsys. However I am
sure that those also come with a cost of having to allocate that memory
and free it.
As the number of file increases vdir gets slower, to the point where it can
become slower the HD.
With Fsys the drawback is the ram disk share the cache with the HD.
Efsys.ram and vdir are nice if you don’t need to run Fsys at all, kind of
overkill just to run a ram disk.
Really if you don’t need an embedded flash filesystem there is no point to
running Efsys.ram. So really the comparison should be between vdir and
the Fsys based ramdisk.I think I covered the pros/cons for vdir above, so for the Fsys based one
(although others may be able to provide further detail). I would say that
Fsys would be faster based upon the fact that it would allocate a static
sized disk, and it wouldn’t have to free and allocate when more is needed.
Also with a Fsys based ramdisk you don’t need to worry about not having
enough memory if there is a bunch of applications running. You will know
how much you have and how much you will have left at all times.Regards,
Erick
Tony <> mts.spb.suxx@mail.ru> > wrote:
On 26 May 2004 12:04:41 GMT, Erick Muis <> emuis@node55.ott.qnx.com
wrote:Unless you have a reason to use Efsys.ram, it is generally best to just
go with the Fsys based ramdisk.
There is yet another utility to have a ram-disk: /bin/vdir
If one compares three of them Efsys.ram, vdir and Fsys based ramdisk,
what
are pros and cons?Tony.
–
Erick Muis
Hardware Group
QNX Software Systems Ltd.
Email: emuis at qnx.com
Mario Charest postmaster@127.0.0.1 wrote:
MC > As the number of file increases vdir gets slower, to the point where it can
MC > become slower the HD.
MC > With Fsys the drawback is the ram disk share the cache with the HD.
MC > Efsys.ram and vdir are nice if you don’t need to run Fsys at all, kind of
MC > overkill just to run a ram disk.
True, but you can run multiple copies of vdir at different mount points.
“Bill Caroselli” <qtps@earthlink.net> wrote in message
news:c9335g$kgu$2@inn.qnx.com…
Mario Charest postmaster@127.0.0.1 wrote:
MC > As the number of file increases vdir gets slower, to the point where
it can
MC > become slower the HD.MC > With Fsys the drawback is the ram disk share the cache with the HD.
MC > Efsys.ram and vdir are nice if you don’t need to run Fsys at all,
kind of
MC > overkill just to run a ram disk.True, but you can run multiple copies of vdir at different mount points.
I meant to say Fsys is overkill
“John Garvey” <jgarvey@qnx.com> wrote in message
news:c932qc$kgd$1@inn.qnx.com…
Mario Charest postmaster@127.0.0.1 wrote:
With Fsys the drawback is the ram disk share the cache with the HD.
No. The ramdisk resides in its own ram area (equal in size to -r
value) and independant of Fsys buffer cache area (-c value). Access
to the ramdisk does not go through this cache.
Cool!
However I think minium cache size is 64K, which in case of ram disk is
wasted. Is a cache allocated if there is no HD driver?
Mario Charest postmaster@127.0.0.1 wrote:
However I think minium cache size is 64K, which in case of ram disk is
wasted. Is a cache allocated if there is no HD driver?
Fsys does not know there will be no HD drivers, so yes it will always
go and allocate some buffer cache (according to -c or default rules).
The minimum is based on number of coroutines (so, yes will be 64k,
you can reduce with -t). If Fsys is being used solely for ramdisk
then you can also reduce memory through other options, such as -C,
-f, -i, -l, -t or -H. But Fsys is not trying to be a streamlined
ramdisk, it is trying to be a disk filesystem which also has a ramdisk.