Read algorithm-raid1/raid10

Read algorithm-raid1/raid10

[Roberto Spadim]

hi guys, could we implement a load_balance read algorithm for SSD?
nearest head isn't as fast as round robin for ssd.
i'm talking about raid1 (raid10 too)
what's my problem?
as i can see, raid0 is faster than raid1
for example:
two disks raid0 is faster than
two disks raid1.

why?
nearest head
instead of a balanced read algorithm (like raid0) the nearest head
make raid1 use only one disk for searchs where we could use two disks
(like raid0)

could we implement a round robin for ssd? and make raid1 as fast as
raid0 for ssd?
i didn't tested the raid10 algorithm yet.
thanks a lot.

-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial

Re: Read algorithm-raid1/raid10

[Roberto Spadim]

like this patch (a long time ago)
http://www.spinics.net/lists/raid/msg30003.html


2011/1/18 Roberto Spadim <roberto@spadim.com.br>:
> hi guys, could we implement a load_balance read algorithm for SSD?
> nearest head isn't as fast as round robin for ssd.
> i'm talking about raid1 (raid10 too)
> what's my problem?
> as i can see, raid0 is faster than raid1
> for example:
> two disks raid0 is faster than
> two disks raid1.
>
> why?
> nearest head
> instead of a balanced read algorithm (like raid0) the nearest head
> make raid1 use only one disk for searchs where we could use two disks
> (like raid0)
>
> could we implement a round robin for ssd? and make raid1 as fast as
> raid0 for ssd?
> i didn't tested the raid10 algorithm yet.
> thanks a lot.
>
> --
> Roberto Spadim
> Spadim Technology / SPAEmpresarial
>



-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial

Re: Read algorithm-raid1/raid10

[Keld Jørn Simonsen]

On Tue, Jan 18, 2011 at 12:00:49PM -0200, Roberto Spadim wrote:
> like this patch (a long time ago)
> http://www.spinics.net/lists/raid/msg30003.html
> 
> 
> 2011/1/18 Roberto Spadim <roberto@spadim.com.br>:
> > hi guys, could we implement a load_balance read algorithm for SSD?
> > nearest head isn't as fast as round robin for ssd.
> > i'm talking about raid1 (raid10 too)
> > what's my problem?
> > as i can see, raid0 is faster than raid1
> > for example:
> > two disks raid0 is faster than
> > two disks raid1.
> >
> > why?
> > nearest head
> > instead of a balanced read algorithm (like raid0) the nearest head
> > make raid1 use only one disk for searchs where we could use two disks
> > (like raid0)
> >
> > could we implement a round robin for ssd? and make raid1 as fast as
> > raid0 for ssd?
> > i didn't tested the raid10 algorithm yet.
> > thanks a lot.

This should only be in use for SSDs. For disks it would be a waste of IO
bandwidth. How do we detect whether it is a SSSD.
Another way to accomplish an improvement os to use the offset layout of
raid10.

best regards
Keld

Re: Read algorithm-raid1/raid10

[Mathias Burén]

2011/1/18 Keld Jørn Simonsen <keld@keldix.com>:
> On Tue, Jan 18, 2011 at 12:00:49PM -0200, Roberto Spadim wrote:
>> like this patch (a long time ago)
>> http://www.spinics.net/lists/raid/msg30003.html
>>
>>
>> 2011/1/18 Roberto Spadim <roberto@spadim.com.br>:
>> > hi guys, could we implement a load_balance read algorithm for SSD?
>> > nearest head isn't as fast as round robin for ssd.
>> > i'm talking about raid1 (raid10 too)
>> > what's my problem?
>> > as i can see, raid0 is faster than raid1
>> > for example:
>> > two disks raid0 is faster than
>> > two disks raid1.
>> >
>> > why?
>> > nearest head
>> > instead of a balanced read algorithm (like raid0) the nearest head
>> > make raid1 use only one disk for searchs where we could use two disks
>> > (like raid0)
>> >
>> > could we implement a round robin for ssd? and make raid1 as fast as
>> > raid0 for ssd?
>> > i didn't tested the raid10 algorithm yet.
>> > thanks a lot.
>
> This should only be in use for SSDs. For disks it would be a waste of IO
> bandwidth. How do we detect whether it is a SSSD.
> Another way to accomplish an improvement os to use the offset layout of
> raid10.
>
> best regards
> Keld
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Hi,

There is a way to check if the device is an SSD or not; the rotational
queue flag in sysfs. See
http://amailbox.org/mailarchive/git-commits-head/2009/1/30/4859834/thread
.

// Mathias
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Read algorithm-raid1/raid10

[Roberto Spadim]

yes i found it in my /sys filesystem, a rotational information 0 for
hd 1 for ssd

i write a long time ago a more interesting algorithm but complex... a
minimal time algorithm, it should have information about head position
time, read time (per bit, per byte, per units....) and calculate the
time to make a read in each disk considering that it could be reading
(time to stop read current requestion) and after this get the smallest
time -> the best read performace

if we use only ssd disk today implementation isn´t good, if we use hdd
maybe a good (if we don´t use 7200rpm + 10000rpm + 15000rpm disks), if
we use a mixed ssd+hdd it will not work very good too... this should
be a per disk optimization (minimal time to read) a round robin is a
good feature (for ssd only) but a mixed array should allow minimal
time algorithm

any idea how to implement a round robin and a algorithm (per raid
device) selection using sysfs?
there´s a patch but i didn´t found information about how to patch the
kernel with it
can anyone help me?
thanks

2011/1/18 Mathias Burén <mathias.buren@gmail.com>:
> 2011/1/18 Keld Jørn Simonsen <keld@keldix.com>:
>> On Tue, Jan 18, 2011 at 12:00:49PM -0200, Roberto Spadim wrote:
>>> like this patch (a long time ago)
>>> http://www.spinics.net/lists/raid/msg30003.html
>>>
>>>
>>> 2011/1/18 Roberto Spadim <roberto@spadim.com.br>:
>>> > hi guys, could we implement a load_balance read algorithm for SSD?
>>> > nearest head isn't as fast as round robin for ssd.
>>> > i'm talking about raid1 (raid10 too)
>>> > what's my problem?
>>> > as i can see, raid0 is faster than raid1
>>> > for example:
>>> > two disks raid0 is faster than
>>> > two disks raid1.
>>> >
>>> > why?
>>> > nearest head
>>> > instead of a balanced read algorithm (like raid0) the nearest head
>>> > make raid1 use only one disk for searchs where we could use two disks
>>> > (like raid0)
>>> >
>>> > could we implement a round robin for ssd? and make raid1 as fast as
>>> > raid0 for ssd?
>>> > i didn't tested the raid10 algorithm yet.
>>> > thanks a lot.
>>
>> This should only be in use for SSDs. For disks it would be a waste of IO
>> bandwidth. How do we detect whether it is a SSSD.
>> Another way to accomplish an improvement os to use the offset layout of
>> raid10.
>>
>> best regards
>> Keld
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
> Hi,
>
> There is a way to check if the device is an SSD or not; the rotational
> queue flag in sysfs. See
> http://amailbox.org/mailarchive/git-commits-head/2009/1/30/4859834/thread
> .
>
> // Mathias
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>



-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Read algorithm-raid1/raid10

[Roberto Spadim]

let´s think about a raid like:

md1 = raid1, /dev/sda (ssd), /dev/sdb (ssd)
md2 = raid1, /dev/sdc (hdd), /dev/sdd (hdd)
md3 = raid0, /dev/md1 (ssd raid), /dev/md2 (hdd raid)

(a raid10 like)

we could make md3 write/read round robin only, and md2/md1 diferent
read/write optimizations


2011/1/18 Roberto Spadim <roberto@spadim.com.br>:
> yes i found it in my /sys filesystem, a rotational information 0 for
> hd 1 for ssd
>
> i write a long time ago a more interesting algorithm but complex... a
> minimal time algorithm, it should have information about head position
> time, read time (per bit, per byte, per units....) and calculate the
> time to make a read in each disk considering that it could be reading
> (time to stop read current requestion) and after this get the smallest
> time -> the best read performace
>
> if we use only ssd disk today implementation isn´t good, if we use hdd
> maybe a good (if we don´t use 7200rpm + 10000rpm + 15000rpm disks), if
> we use a mixed ssd+hdd it will not work very good too... this should
> be a per disk optimization (minimal time to read) a round robin is a
> good feature (for ssd only) but a mixed array should allow minimal
> time algorithm
>
> any idea how to implement a round robin and a algorithm (per raid
> device) selection using sysfs?
> there´s a patch but i didn´t found information about how to patch the
> kernel with it
> can anyone help me?
> thanks
>
> 2011/1/18 Mathias Burén <mathias.buren@gmail.com>:
>> 2011/1/18 Keld Jørn Simonsen <keld@keldix.com>:
>>> On Tue, Jan 18, 2011 at 12:00:49PM -0200, Roberto Spadim wrote:
>>>> like this patch (a long time ago)
>>>> http://www.spinics.net/lists/raid/msg30003.html
>>>>
>>>>
>>>> 2011/1/18 Roberto Spadim <roberto@spadim.com.br>:
>>>> > hi guys, could we implement a load_balance read algorithm for SSD?
>>>> > nearest head isn't as fast as round robin for ssd.
>>>> > i'm talking about raid1 (raid10 too)
>>>> > what's my problem?
>>>> > as i can see, raid0 is faster than raid1
>>>> > for example:
>>>> > two disks raid0 is faster than
>>>> > two disks raid1.
>>>> >
>>>> > why?
>>>> > nearest head
>>>> > instead of a balanced read algorithm (like raid0) the nearest head
>>>> > make raid1 use only one disk for searchs where we could use two disks
>>>> > (like raid0)
>>>> >
>>>> > could we implement a round robin for ssd? and make raid1 as fast as
>>>> > raid0 for ssd?
>>>> > i didn't tested the raid10 algorithm yet.
>>>> > thanks a lot.
>>>
>>> This should only be in use for SSDs. For disks it would be a waste of IO
>>> bandwidth. How do we detect whether it is a SSSD.
>>> Another way to accomplish an improvement os to use the offset layout of
>>> raid10.
>>>
>>> best regards
>>> Keld
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>
>> Hi,
>>
>> There is a way to check if the device is an SSD or not; the rotational
>> queue flag in sysfs. See
>> http://amailbox.org/mailarchive/git-commits-head/2009/1/30/4859834/thread
>> .
>>
>> // Mathias
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
>
>
> --
> Roberto Spadim
> Spadim Technology / SPAEmpresarial
>



-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html