zfs discuss - Aug 2009 - ?: SMI vs. EFI label and a disk''s write cache

For Solaris 10 5/09...

There are supposed to be performance improvements if you create a zpool 
on a full disk, such as one with an EFI label. Does the same apply if 
the full disk is used with an SMI label, which is required to boot?

I am trying to determine the trade-off, if any, of having a single rpool 
on cXtYd0s2, if I can even do that, and improved performance compared to 
having two pools, a root pool and a separate data pool, for improved 
manageability and isolation. The data pool will have zone root paths on 
it. Customer has stated they are experiencing some performance limits in 
their application due to the disk, and if creating a single pool will 
help by enabling the write cache, that may be of value.

If the *current* answer is no to having ZFS turn on the write cache at 
this time, is it something that is coming in OpenSolaris or an update to 
S10?

Thanks
Steffen

Hi Steffen,

Go with a mirrored root pool is my advice with all the disk space in s0
on each disk. Simple is best and redundant simple is even better.

I''m no write cache expert, but a few simple tests on Solaris 10 5/09,
show me that the write cache is enabled on a disk that is labeled with
an SMI label and slice when the pool is created, if the whole disk''s 
capacity is in slice 0, for example. However, its not enabled on my
s10u7 root pool slice, all disk space is in slice 0, but it is enabled
on my upcoming Solaris 10 root pool disk. Don''t know what''s up
with
that.

If performance is a goal then go with two pools anyway so that you have
more flexibility in configuring a mirrored or RAID-Z config for the data 
pool or adding log devices (if that helps their workload) and also
provides more flexibility in management of ZFS BEs vs ZFS data in zones, 
and so on.

With a root pool, you currently constrained by no RAID-Z, can''t add 
add''l mirrored VDEVs, no log devices, can''t be exported to
another
system, and so on.

The ZFS BP wiki provides more performance-related tips:

http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide

Cindy

On 08/05/09 15:07, Steffen Weiberle wrote:
> For Solaris 10 5/09...
> 
> There are supposed to be performance improvements if you create a zpool 
> on a full disk, such as one with an EFI label. Does the same apply if 
> the full disk is used with an SMI label, which is required to boot?
> 
> I am trying to determine the trade-off, if any, of having a single rpool 
> on cXtYd0s2, if I can even do that, and improved performance compared to 
> having two pools, a root pool and a separate data pool, for improved 
> manageability and isolation. The data pool will have zone root paths on 
> it. Customer has stated they are experiencing some performance limits in 
> their application due to the disk, and if creating a single pool will 
> help by enabling the write cache, that may be of value.
> 
> If the *current* answer is no to having ZFS turn on the write cache at 
> this time, is it something that is coming in OpenSolaris or an update to 
> S10?
> 
> Thanks
> Steffen
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss

Hi Cindy, thanks for the reply...

On 08/05/09 18:55, Cindy.Swearingen at Sun.COM wrote:
> Hi Steffen,
> 
> Go with a mirrored root pool is my advice with all the disk space in s0
> on each disk. Simple is best and redundant simple is even better.
I will suggest that. Had already considered it. Since they may be forced 
to do a fresh load, they could turn off the HW RAID that is currently in 
place. System are T5xy0s.

> I''m no write cache expert, but a few simple tests on Solaris 10
5/09,
> show me that the write cache is enabled on a disk that is labeled with
> an SMI label and slice when the pool is created, if the whole
disk''s
> capacity is in slice 0, for example. 
Was that a performance test or a status test using something like format -e?

Turns out I am trying this on an ATA drive, and format -e doesn''t do 
anything there.

 > However, its not enabled on my
> s10u7 root pool slice, all disk space is in slice 0, but it is enabled
> on my upcoming Solaris 10 root pool disk. Don''t know
what''s up with
> that.
And I don''t fully follow, since 5/09 is update 7 :)

Now maybe I do. The former case is a non-root pool and the latter is a 
root pool?
> If performance is a goal then go with two pools anyway so that you have
> more flexibility in configuring a mirrored or RAID-Z config for the data 
> pool or adding log devices (if that helps their workload) and also
> provides more flexibility in management of ZFS BEs vs ZFS data in zones, 
> and so on.
System has two drives, so I don''t see how I/they could get more 
performance by using RAID, at least for the write side of things (and I 
don''t know where the performance issue is).

My other concern with two pools on a single disk is there less 
likelihood of putting two unrelated writes close together if they are in 
different pools, not just different file systems/data sets in the same 
pool. So two pools might force considerably more head movements--across 
more of the platter.
> With a root pool, you currently constrained by no RAID-Z, can''t
add
> add''l mirrored VDEVs, no log devices, can''t be exported
to another
> system, and so on.
These would be internal disks. Good point about the lack of log 
devices--not sure if there might be interest or opportunity in adding 
SSD later.
> The ZFS BP wiki provides more performance-related tips:
> 
> http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide
Ah, and I only looked on the Evil Tuning Guide one. The BP mentions the 
whole disk, however it is not clear whether that applies to the root, 
non-EFI pool, so your information is of value to me.

Steffen
> 
> Cindy
> 
> On 08/05/09 15:07, Steffen Weiberle wrote:
>> For Solaris 10 5/09...
>>
>> There are supposed to be performance improvements if you create a 
>> zpool on a full disk, such as one with an EFI label. Does the same 
>> apply if the full disk is used with an SMI label, which is required to 
>> boot?
>>
>> I am trying to determine the trade-off, if any, of having a single 
>> rpool on cXtYd0s2, if I can even do that, and improved performance 
>> compared to having two pools, a root pool and a separate data pool, 
>> for improved manageability and isolation. The data pool will have zone 
>> root paths on it. Customer has stated they are experiencing some 
>> performance limits in their application due to the disk, and if 
>> creating a single pool will help by enabling the write cache, that may 
>> be of value.
>>
>> If the *current* answer is no to having ZFS turn on the write cache at 
>> this time, is it something that is coming in OpenSolaris or an update 
>> to S10?
>>
>> Thanks
>> Steffen
>> _______________________________________________
>> zfs-discuss mailing list
>> zfs-discuss at opensolaris.org
>> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss