I''ve looked on the mailing list (the evil tuning wikis are down) and haven''t seen a reference to this seemingly simple question... I have two OCZ Vertex 4 SSDs acting as L2ARC. I have a spare Crucial SSD (about 1.5 years old) that isn''t getting much use and i''m curious about adding it to the pool as a third L2ARC device. Is there any reason why I technically can''t use different capacity and/or manufacturer SSDs as a single ZFS pool''s L2ARC? Even if it will work technically, will this configuration negatively impact performance (e.g. slow down the entire cache to the slowest drive''s performance)? Thanks! Matt -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20120926/1545a3b4/attachment.html>
On 09/26/2012 05:08 PM, Matt Van Mater wrote:> I''ve looked on the mailing list (the evil tuning wikis are down) and > haven''t seen a reference to this seemingly simple question... > > I have two OCZ Vertex 4 SSDs acting as L2ARC. I have a spare Crucial SSD > (about 1.5 years old) that isn''t getting much use and i''m curious about > adding it to the pool as a third L2ARC device. > > Is there any reason why I technically can''t use different capacity and/or > manufacturer SSDs as a single ZFS pool''s L2ARC?No, there isn''t. You can do it without problems.> Even if it will work technically, will this configuration negatively impact > performance (e.g. slow down the entire cache to the slowest drive''s > performance)?If the added device is slower, you will experience a slight drop in per-op performance, however, if your working set needs another SSD, overall it might improve your throughput (as the cache hit ratio will increase). Cheers, -- Saso
> > If the added device is slower, you will experience a slight drop in > per-op performance, however, if your working set needs another SSD, > overall it might improve your throughput (as the cache hit ratio will > increase). >Thanks for your fast reply! I think I know the answer to this question, but what is the best way to determine how large my pool''s l2arc working set is (i.e. how much l2arc is in use)? Matt -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20120926/e17bc7f1/attachment.html>
On 09/26/2012 05:18 PM, Matt Van Mater wrote:>> >> If the added device is slower, you will experience a slight drop in >> per-op performance, however, if your working set needs another SSD, >> overall it might improve your throughput (as the cache hit ratio will >> increase). >> > > Thanks for your fast reply! I think I know the answer to this question, > but what is the best way to determine how large my pool''s l2arc working set > is (i.e. how much l2arc is in use)?Go grab arcstat.pl from http://blog.harschsystems.com/2010/09/08/arcstat-pl-updated-for-l2arc-statistics/ - that''s the tool you''re looking for. Cheers, -- Saso
Dan Swartzendruber
2012-Sep-26 15:21 UTC
[zfs-discuss] Different size / manufacturer L2ARC
On 9/26/2012 11:18 AM, Matt Van Mater wrote:> > If the added device is slower, you will experience a slight drop in > per-op performance, however, if your working set needs another SSD, > overall it might improve your throughput (as the cache hit ratio will > increase). > > > Thanks for your fast reply! I think I know the answer to this > question, but what is the best way to determine how large my pool''s > l2arc working set is (i.e. how much l2arc is in use)? >Easiest way: zpool iostat -v -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20120926/528dd992/attachment.html>
Excellent thanks to you both. I knew of both those methods and wanted to make sure i wasn''t missing something! On Wed, Sep 26, 2012 at 11:21 AM, Dan Swartzendruber <dswartz at druber.com>wrote:> ** > On 9/26/2012 11:18 AM, Matt Van Mater wrote: > > If the added device is slower, you will experience a slight drop in >> per-op performance, however, if your working set needs another SSD, >> overall it might improve your throughput (as the cache hit ratio will >> increase). >> > > Thanks for your fast reply! I think I know the answer to this question, > but what is the best way to determine how large my pool''s l2arc working set > is (i.e. how much l2arc is in use)? > > > Easiest way: > > zpool iostat -v > > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20120926/29c3c1b0/attachment.html>