Date: Sun, 16 Oct 2011 21:09:53 +0300 From: Daniel Kalchev <daniel@digsys.bg> To: "Luchesar V. ILIEV" <luchesar.iliev@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: [ZFS] Using SSD with partitions Message-ID: <14628DFB-AA3E-4D2D-9D4F-723B6327B6C0@digsys.bg> In-Reply-To: <4E9B1C1E.7090804@gmail.com> References: <CACh33Fpz=uAp8h0Bjsi1Be=ob_94jXtN51mAHvGPkReY5MpTcg@mail.gmail.com> <4E9AE725.4040001@gmail.com> <169E82FD-3B61-4CAB-B067-D380D69CDED5@digsys.bg> <4E9B1C1E.7090804@gmail.com>
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On Oct 16, 2011, at 21:02 , Luchesar V. ILIEV wrote: > On 16/10/2011 19:17, Daniel Kalchev wrote: >> Therefore, with ZFS v28, adding ZIL does not introduce any more risk >> to your data. >=20 > I might be wrong in my interpretation, but from what I remember, when > the power goes down, an unprotected SSD is likely to lose _more_ data > than simply its write buffers -- that's quite unlike a hard-drive. So > much, in fact, that the whole ZIL might become corrupted (and that's > potentially way more data than any device cache). The real risk with low-grade "unprotected" SSDs is that the SSD may well = become damaged, sometimes beyond repair. It is the same risk with SSDs or with magnetic drives. If the drive lies = to the OS that it has safely written data -- then data will be lost. = Thing is, we know what a cheap HDD is. Most SSDs however lie, because = otherwise they will offer very poor write performance. ZIL is not about RAM. ZIL is for low latency synchronous writing. It = does not matter how much RAM do you have -- it will not help if you have = heavy synchronous writing (of small records). =20 Anyway, as it was mentioned -- with moderate activity on the pool, it is = not problem to use the same SSD for boot/ZIL/L2ARC. Daniel=
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