Hi, I''ve ordered a new server with: - 4x600GB Toshiba 10K SAS2 Disks - 2x100GB OCZ DENEVA 2R SYNC eMLC SATA (no expander so I hope no SAS/ SATA problems). Specs: http://www.oczenterprise.com/ssd-products/deneva-2-r-sata-6g-2.5-emlc.html I want to use the 2 OCZ SSDs as mirrored intent log devices, but as the intent log needs quite a small amount of the disks (10GB?), I was wondering if I can use the rest of the disks as L2ARC? I have a few questions about this: -Is 10GB enough for a log device? -Can I partition the disks (10GB + 90 GB) and use the unused (90GB) space as L2ARC? -If I use the rest of the disks as L2ARC, do I have to mirror the L2ARC or can I just add 2 partitions (eg: 2 x 90GB = 180GB) -If I used non mirrored L2ARC, Could something go wrong if one L2ARC device failed (pool unavailable,lock in the kernel, panic,...)? -- Michel Jansens
On 11/14/2012 11:14 AM, Michel Jansens wrote:> Hi, > > I''ve ordered a new server with: > - 4x600GB Toshiba 10K SAS2 Disks > - 2x100GB OCZ DENEVA 2R SYNC eMLC SATA (no expander so I hope no > SAS/SATA problems). Specs: > http://www.oczenterprise.com/ssd-products/deneva-2-r-sata-6g-2.5-emlc.html > > I want to use the 2 OCZ SSDs as mirrored intent log devices, but as the > intent log needs quite a small amount of the disks (10GB?), I was > wondering if I can use the rest of the disks as L2ARC? > > I have a few questions about this: > > -Is 10GB enough for a log device?A log device, essentially, only needs to hold a single transaction''s-worth of small sync writes, so unless you write more than that, you''ll be fine. In fact, DDRdrive''s X1 is only 4GB and works just fine.> -Can I partition the disks (10GB + 90 GB) and use the unused (90GB) > space as L2ARC?Yes, you can.> -If I use the rest of the disks as L2ARC, do I have to mirror the L2ARC > or can I just add 2 partitions (eg: 2 x 90GB = 180GB)L2ARC doesn''t have mirroring, it''s always striped.> -If I used non mirrored L2ARC, Could something go wrong if one L2ARC > device failed (pool unavailable,lock in the kernel, panic,...)?No, an L2ARC only holds non-dirty data from the main storage pool for quick access, so if a read to an L2ARC device fails (due to it failing, being removed, or returning bad data), then the read is simply reissued to the main pool drives transparently (and fault-management kicks in to handle the problem with the L2ARC, such as taking it offline, etc.). Cheers, -- Saso
On 14 November, 2012 - Michel Jansens sent me these 1,0K bytes:> Hi, > > I''ve ordered a new server with: > - 4x600GB Toshiba 10K SAS2 Disks > - 2x100GB OCZ DENEVA 2R SYNC eMLC SATA (no expander so I hope no SAS/ > SATA problems). Specs: > http://www.oczenterprise.com/ssd-products/deneva-2-r-sata-6g-2.5-emlc.html > > I want to use the 2 OCZ SSDs as mirrored intent log devices, but as the > intent log needs quite a small amount of the disks (10GB?), I was > wondering if I can use the rest of the disks as L2ARC? > > I have a few questions about this: > > -Is 10GB enough for a log device?Our log device for the department file server, for roughly 100 workstations etc, seems to hover about 2MB used. It''s only sync writes that goes here, and it''s emptied at the next transaction. So check how much sync writes you have per flush (normally 5 seconds nowadays, used to be 30 I think?). If you are pushing more than 2GB of sync operations per second, then I think you should get something beefier ;)> -Can I partition the disks (10GB + 90 GB) and use the unused (90GB) > space as L2ARC? > -If I use the rest of the disks as L2ARC, do I have to mirror the L2ARC > or can I just add 2 partitions (eg: 2 x 90GB = 180GB) > -If I used non mirrored L2ARC, Could something go wrong if one L2ARC > device failed (pool unavailable,lock in the kernel, panic,...)?It''s checksummed and verified, shouldn''t be a problem even if it fails (could be a problem if it''s half-failing and just being slow, if so - get rid of it).> > > -- > Michel Jansens > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss/Tomas -- Tomas Forsman, stric at acc.umu.se, http://www.acc.umu.se/~stric/ |- Student at Computing Science, University of Ume? `- Sysadmin at {cs,acc}.umu.se
On 11/14/12 03:24, Sa?o Kiselkov wrote:> On 11/14/2012 11:14 AM, Michel Jansens wrote: >> Hi, >> >> I''ve ordered a new server with: >> - 4x600GB Toshiba 10K SAS2 Disks >> - 2x100GB OCZ DENEVA 2R SYNC eMLC SATA (no expander so I hope no >> SAS/SATA problems). Specs: >> http://www.oczenterprise.com/ssd-products/deneva-2-r-sata-6g-2.5-emlc.html >> >> I want to use the 2 OCZ SSDs as mirrored intent log devices, but as the >> intent log needs quite a small amount of the disks (10GB?), I was >> wondering if I can use the rest of the disks as L2ARC? >> >> I have a few questions about this: >> >> -Is 10GB enough for a log device? > A log device, essentially, only needs to hold a single > transaction''s-worth of small sync writes,Actually it needs to hold 3 transaction groups worth. There are 3 phases to ZFS''s transaction group model: open, quiescing and syncing. Nowadays the sync phase is targetted at 5s so the log device needs to be able to hold up to 15s of synchronous data.> so unless you write more than > that, you''ll be fine. In fact, DDRdrive''s X1 is only 4GB and works just > fine.Agreed, 10GB should be fine for your system. Neil.