On Jan 31, 2010, at 7:21 AM, Henrik Johansson wrote:
> Hello Christo,
>
> On Jan 31, 2010, at 4:07 PM, Christo Kutrovsky wrote:
>
>> Hello All,
>>
>> I am running NTFS over iSCSI on a ZFS ZVOL volume with compression=gzip-9
>> and blocksize=8K. The server is 2 core P4 3.0 Ghz with 5 GB of RAM.
For NTFS, use recordsize=4 KB, but I wouldn't worry too much about compression
at
that recordsize.
>> Whenever I start copying files from Windows onto the ZFS disk, after about
>> 100-200 Mb been copied the server starts to experience freezes. I have
>> iostat running, which freezes as well. Even pings on both of the network
>> adapters are reporting either 4000 ms or timeouts for when the freeze is
>> happening.
>>
>> I have reproduce the same behavior with a 1 GB test ZVOL. Whenever I do
>> sequential writes of 64 Kb with compression=gzip-9 I experience the freezes.
>> With compression=off it's all good.
gzip-9 is a pig. b115 includes the fix for:
CR6586537 async zio taskqs can block out userland commands
which greatly reduced this effect. But you might consider the default gzip-6
instead.
Back to my note above, compression is done to records, but the size is still
512 byte sectors. In other words, there are 8 sectors in a 4 KB record, so
compression is bounded by 12.5% chunks.
>> I've also experienced similar behavior (short freezes) when running zfs
>> send|zfs receive with compression on LOCALLY on ZVOLs again.
>
> I think gzip in ZFS have a reputation being somewhat heavy on system
> resources, that said it would be nice if it did not have such a large impact
> on low level functions. Have a look in the archive, search for example
> death-spriral or Death-spriral revisited. Have you tried using the default
> compression algorithm also (lzjb, compresison=on)?
Good idea, and for small records compression gains less.
-- richard
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
