Hi all, Sorry for spamming your mailinglist, but since I could not find a direct awnser on the internet and archives, I give this a try! I am building an ZFS filesystem to export iSCSI LUN''s. Now I was wondering if the L2ARC has the ability to cache non-filesystem iscsi lun''s? Or does it only work in combination with the ZFS mounted filesystem? Next to that I am reading all kind of performance benefits using seperate devices for the ZIL (write) and the Cache (read). I was wondering if I could share a single SSD between both ZIL and Cache device? Or is this not recommended? This because the ZIL needs 1 GB top from what I read? But since SSD is not cheap, I would like to make use of the other GB''s on the disk. Thank you. Armand -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20100111/c8b9af71/attachment.html>
> > Next to that I am reading all kind of performance benefits using seperate > devices > for the ZIL (write) and the Cache (read). I was wondering if I could > share a single SSD between both ZIL and Cache device? > > Or is this not recommended? > > > i asked something similar recently. The answers i got were along theselines: you can use a single ssd but it''s not a great idea. If you DO need to use a single ssd for such a thing, make sure it''s one of the more expensive SLC variety like the intel x25-e The MLC variety of SSD works well for L2ARC and is much cheaper (you can pick up some for less than 100 bucks) while the ZIL really should have the SLC variety. I''m not an expert though, i''m just passing on advice i''ve been given. For reads and dedup L2ARC does make a dramatic difference, and for NFS and database stuff an SSD ZIL will make a huge difference. I''ve heard of people getting 5-10x''s performance increase on reads just by adding a cheap ssd so i''d say it''s worth it if that''s the type of dataset you have. Another thing i was told on more than one occasion was that you may not even NEED a ssd for your ZIL (basically you should run a script to see if you need a ZIL at all, i don''t remember where this script is but i''m SURE someone will reply with it) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20100110/ce481c85/attachment.html>
Hi ; I dont think that anyone owns the list and as anyone else you are very welcome to ask any question. L2arc will cache zpool so if your iscs lun is a zvol or a file on zfs it will be cached. Please use constar if you need performance You are correct that you will only need couple of gb as zil. Performance gain of using a portion of ssd for l2arc will depend on your pool configuration, your average load mix. A side note: use raid 10 if you are using zfs and iscsi and need random iops Best regards Mertol Sent from a mobile device Mertol Ozyoney On 11.Oca.2010, at 01:05, "A. Krijgsman" <a.krijgsman at draftsman.nl> wrote:> Hi all, > > Sorry for spamming your mailinglist, > but since I could not find a direct awnser on the internet and > archives, I give this a try! > > I am building an ZFS filesystem to export iSCSI LUN''s. > Now I was wondering if the L2ARC has the ability to cache non- > filesystem iscsi lun''s? > Or does it only work in combination with the ZFS mounted filesystem? > > Next to that I am reading all kind of performance benefits using > seperate devices > for the ZIL (write) and the Cache (read). I was wondering if I could > share a single SSD between both ZIL and Cache device? > > Or is this not recommended? > > This because the ZIL needs 1 GB top from what I read? > But since SSD is not cheap, I would like to make use of the other > GB''s on the disk. > > Thank you. > > Armand > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20100111/931112cb/attachment.html>
Thank you Thomas and Mertol for your feedback.
I was indeed aiming for the x25-E because of their write performance.
However since these are around 350? for 32 GB I find it disturbing to only use
it for ZIL :-)
I will do some tests with a cheap MLC disk.
I also read about the disk cache needing to be disabled to avoid dataloss after
a powerloss.
If a journaling FS is run over iscsi this should not become an issue right?
( Or will ZFS be affected by missing data from cache? )
Since I am hanging here now:
Do people experience trouble on exporting iscsi zvol''s with their
cpu-load because of the TCP-IP calculations?
Or is is safe to ignore the TOE network cards?
Regards,
Armand
----- Original Message -----
From: Thomas Burgess
To: A. Krijgsman
Cc: zfs-discuss at opensolaris.org
Sent: Monday, January 11, 2010 3:02 AM
Subject: Re: [zfs-discuss] ZFS Cache + ZIL on single SSD
Next to that I am reading all kind of performance benefits using seperate
devices
for the ZIL (write) and the Cache (read). I was wondering if I could
share a single SSD between both ZIL and Cache device?
Or is this not recommended?
i asked something similar recently. The answers i got were along these lines:
you can use a single ssd but it''s not a great idea. If you DO need
to use a single ssd for such a thing, make sure it''s one of the more
expensive SLC variety like the intel x25-e
The MLC variety of SSD works well for L2ARC and is much cheaper (you can pick
up some for less than 100 bucks) while the ZIL really should have the SLC
variety.
I''m not an expert though, i''m just passing on advice
i''ve been given.
For reads and dedup L2ARC does make a dramatic difference, and for NFS and
database stuff an SSD ZIL will make a huge difference.
I''ve heard of people getting 5-10x''s performance increase on
reads just by adding a cheap ssd so i''d say it''s worth it if
that''s the type of dataset you have.
Another thing i was told on more than one occasion was that you may not even
NEED a ssd for your ZIL (basically you should run a script to see if you need a
ZIL at all, i don''t remember where this script is but i''m SURE
someone will reply with it)
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